From vancleef@bga.com Thu Dec 15 02:19:54 EST 1994 From: vancleef@bga.com (Henry van Cleef) Subject: FAQ rec.antiques.radio+phone (part 1 of 5) Date: 14 Dec 1994 01:24:26 -0600 Lines: 342 Message-ID: <3cm6ja$1o7@ivy.bga.com> Summary: Part 1 - Introduction to the FAQ and general questions. Rec.antiques.radio+phono Frequently Asked Questions Revision Date Notes 1.1 Oct. 20, 94. Second version---major editing. Added two new sections for sources-of-supply list. 1.2 Dec. 10, 1994. Minor corrections and revisions. Part 1 - Introduction to the FAQ ------------------------------------------------------------------------------ FAQ editor: Hank van Cleef. Email vancleef@bga.com, vancleef@tmn.com This is a regular posting of frequently-asked questions (FAQ) about antique radios and phonographs. It is intended to summarize some common questions on old home entertainment audio equipment and provide answers to these questions. Regular FAQ postings can help save network bandwidth and maintain a good signal-to-noise ratio in the newsgroup. However, they can't do it alone - you, the reader, have to use them. * If you are a new user, please print and review the FAQ articles and look at the instructions in the news.announce.newusers newsgroup before posting any articles. If you don't find the answer in the FAQ and you have tried elsewhere, then you have "done your homework" and it is acceptable to ask the question on the UseNet newsgroups. Along with your question, please state where else you have looked for the answer so others also know that you have done your homework. * If you are an experienced user, please help by refraining from answering frequently-asked questions on the newsgroup if they are already answered by the FAQ articles. Instead, send e-mail to the user who asked the question. (It will be helpful if you include the part of the FAQ that answers their question, but not the whole thing.) The FAQ cannot always prevent people from posting repetitive questions. But even if hundreds of questions get posted, it saves you from having to answer them hundreds of times. Also, a friendly pointer to the FAQ in your first answer can help that person refer to the FAQ in the future. That is when we can begin to get a real savings of network bandwidth. To reduce the size of articles, the FAQ information is posted in 5 parts: Part 1 - Introduction to the FAQ and general questions. (Editor: Hank van Cleef, vancleef@bga.com; also parts 3 and 5). Part 2 - General questions about acoustical phonographs. (Editor: George Conklin, george@nccu.edu) Part 3 - General questions about vacuum tube radios and phonos. Part 4 - Sources of spares and services for old radios. (Editor: Aaron Field, a.field@uicvm.ui.edu) Part 5. - Frequently-asked technical questions about vacuum tube electronics. Please do not E-mail technical questions, requests to identify various items, or technical questions to the Faq editors. Post them to the newsgroup instead. You will get better answers more quickly by posting. The charter for the rec.antiques.radios+phonos follows immediately, after which are some of the top frequently-asked questions. Newsgroups line: rec.antiques.radio+phono Audio devices and materials of yesteryear. CHARTER Discussion of the use, repair, and collecting of early standard-broadcast radios, phonographs, and any other similarly-related items designed for home entertainment sound receiving or sound reproduction. This group is intended to be a forum for those with an interest in sound-receiving and sound-reproduction equipment that was generally manufactured prior to the widespread use of transistors. The group's discussion, however, will not be strictly limited to vacuum-tube and mechanical devices, and those with an interest in early transistor radios, early televisions, and other such items that reflect pioneering audio technology will be welcomed. Exclusions: Amateur radio equipment discussion will be directed to the existing amateur radio newsgroups and to the boatanchors list. This is only done because those groups present an established forum for people with an interest in classic amateur radio equipment. Those classic amateur radio collectors who also share an interest in early standard-broadcast equipment will fully appreciate the desire to separate the two interests. Their valuable expertise will, however, be most welcome in all forums. Since the summer of 1993, there has been an ongoing discussion among those interested in antique radios and phonographs (and other related equipment and materials) about the possibility of forming this newsgroup. That small core of enthusiasts has rapidly grown in number, and now includes representatives of museums, technical specialists, collectors, and novices with an inquisitiveness about sound reproducing and receiving equipment of the past. With enthusiasm for the preservation and enjoyment of these superb expressions of human inventiveness steadily increasing, the time has come to establish a forum through which knowledge of their history, restoration, and use can be shared by experts and newcomers alike. This proposal represents the essence of what an Internet newsgroup can accomplish--it can produce a collective source of knowledge from which useful information can be drawn for years into the future. Bill Robie, August, 1994 In general, this means: 1. This newsgroup has the name "antique" in it, and primarily addresses home entertainment equipment. It is not a "catch-all" group for discussing things not covered by other groups. 2. Items of particular interest to readers in this group: a. Acoustic phonographs of all types. b. Early electronic phonographs, primarily for playing 78 RPM disks. c. Radios of the 1920-50's period. Of particular interest are Atwater Kent, Philco, and Zenith sets, although all radios by earlier manufacturers are of interest to the group. 3. While much of the discussion the group is about radios and phonos of US manufacture, we welcome discussion of non-US radios and phonos from the same period sold primarily to a domestic market. 4. There are a great many opinions about what is "antique" and what isn't. The focus of the discussion that led to creation of this newsgroup was on phonograph and radio technology of the 1890-1950 era. The group does include some discussion of: a. Monaural vacuum tube "high fidelity" equipment. b. A few early hybrid and transistor home entertainment designs. c. Early black and white televisions, and a few color sets. However, post-1950's technology generally diverges from the focus of this newsgroup. 5. While not originally sold as "home entertainment" equipment, there is an interest in jukeboxes, early musical devices such as the Hammond organ, and movie theater audio, particuarly items manufactured before WW II. 6. While we welcome participation by "hams," and include some discussion of old tube-type communications receivers, particularly from the '30's and '40's in this group, amateur radio issues in general are already well-covered by the rec.radio.amateur groups. The mail list, boatanchors@gnu.ai.mit.edu, is regularly read by people prepared to discuss transmitters, AM operation, etc. Some of the things that don't seem to fit well with this group are: 1. Stereo from the 60's and later, particularly things with bookshelf speakers. 2. Computers (Usenet has hundreds of newsgroups devoted to computers, including old ones. 3. Equipment built primarily for export rather than for domestic sale. 4. Tape recorders other than vacuum tube reel-to-reel units. 5. Video recorders. 6. Guitar amplifiers and other electronic music devices in general, 7. Amateur radio equipment except for older general coverage receivers that sold to non-hams as home entertainment SWL (shortwave listening) sets. The above are general guidelines, not hard-and-fast rules. If you receive a response posting or E-mail indicating that your post was off topic, it will generally point to a more appropriate group. This group has been historically free of flames. There are some very honest differences of opinion about many topics, and some of the discussions are lively. Q. What other newsgroups cover similar items? A. There are several newsgroups covering broadcast and amateur radio. There are also groups covering modern audio equipment. Notable among these are: rec.radio.swap Buy and sell any electronic equipment, new or old. This includes test equipment and accessories. rec.radio.amateur.equipment Specific to ham radio equipment. rec.radio.shortwave Discusses shortwave programming, stations, and receivers. sci.electronics.repair Repair information, primarily for modern equipment. rec.audio.* Discussion of audio equipment. This hierarchy includes several categories, as well as a marketplace newsgroup. Q. Where can I get needles for my Victrola. A. Contact the Antique Phonograph Supply Company, Route 23, Box 123, Davenport Center, NY 13751. Phone 607-278-6218. Remember to change your needles after every play. The engineering concept was simple: the needles are softer than the record, and will wear without stressing the record. Some records had grit in the mix to wear the steel needle. Q. I would like to get an old radio or an old phonograph. Where can I find one? A. Generally, these items are where you find them. There are dealers who specialize in old radios and old phonographs, and these may be the best source if you want something that has been restored to good working condition as well as cosmetically. Second hand stores and thrift shops, estate sales, moving sales, garage sales all can produce interesting items, and it is possible to find some real bargains. Keep in mind that the source of supply is attics, barns, storerooms, where these were tucked away, maybe as much as fifty or seventy years ago. They may or may not have been working when they were stored. Keep in mind that acoustical phonographs have parts in their reproducers that deteriorate over time, and that lubricants deteriorate as well. Electronic equipment also has components that deteriorate over time as well. What you are looking at may have been stored in working condition forty or fifty years ago, and look clean as a whistle, but be in need of major work before you can use it. Q. I found an EtherSnarf model YU4Q radio at an estate auction and got it for $125. Did I get rooked? It looks complete, has ten tubes and a big oak cabinet with spool legs and lots of gewgaws, and has four shortwave bands. I don't find it listed in any old radio buyers' guide. A. First of all, keep in mind that there were literally hundreds of radio manufacturers in the US in the 1920-1960 era, and there were some manufactures who built "trade" radios to be sold under a store's brand name. Part 3 of this FAQ will help you figure out when this radio was built, even if it isn't listed in any of the buyers' manuals or in any of the maintenance manuals that were published at the time. What an old radio is actually worth depends on many things. First of all, what is it worth to you? While there is supposedly a market out there, what a specific radio is actually worth is, in reality, what someone is willing to pay to buy it from you. You want to keep in mind the following: a. The radio may need a good deal of work before it will operate as it was designed to operate. b. Most radios were "lo-fi" in modern terms. Many of us actually enjoy the sound, and many of the consoles, cathedrals, and tombstones were tuned very nicely to the programs sources of the day. c. While the number of tubes may give some indication of the quality of the radio, and a big console cabinet is more likely to house a good radio than a plastic table cabinet, keep in mind that "number of tubes" and "big cabinet" both were selling points in the 1930-50 era that meant "high retail price." Some mid-priced consoles look as though they have a lot more radio in them than they do. Some people swear by the Bunis "Collectors' Guide to Old Radios" series written by Marty and Sue Bunis. Others do not feel that their prices are particularly supportable when trying to sell. Most collectors do not buy for resale, and buy because they want the item. Q. My neighbor's grandfather left him a Victor spring-powered phonograph he wants to sell me for $100. Should I buy it? A. As with old radios, the "worth" of an old phonograph is its "worth to you." There are "price guides" and general ideas of what things can be bought and sold for. However, there are substantial variables, such as geographic location, condition of the unit, etc. Keep in mind that you are going to need some records to play on your machine, and that they are also definitely "lo-fi." Edison fought electrification to the bitter end, so some of the later Edisons, as well as the Victor Orthophonic of the mid-twenties, did incredibly well. Q. I got an old Westinghouse cathedral radio from my neighbor when he cleaned out it his attic. He told me he put it up there when Fred Allen left radio, but that it was working when he stored it. I plugged it in and turned it on. All of the tubes glowed, but nothing came out of the loudspeaker. After a few minutes, one of the tubes got very red inside and then, suddenly, liquid shot out of one of the aluminum cans, hit the bright red tube, and it broke. When I turned the set off, it was smoking, and this liquid got all over everything like tom cat pee. What do I do now? A. Never ever plug in an old piece of electronics gear that hasn't been used for a few years without checking it out first. Part 4 of this FAQ describes some of the things to check. Fred Allen left radio in 1949, so that radio has been stored 45 years. DON'T PLUG IT IN UNTIL YOU HAVE CHECKED IT OUT! What I am describing here actually happened to me around 1948. The problem was a shorted wet electrolytic condenser. The plates of the rectifier tube, an 80, glowed red, and I shut the radio off, but the electrolytic boiled, squirted the electrolyte (nasty stuff) onto the 80, which promptly shattered. Cleanup was a soap-and-water job. Q. Can I get spares for restoring my Edison phonograph---for my Atwater Kent radio. A. Parts 2 and 4 of this FAQ list suppliers of spares for phonos and radios, respectively. In addition to spares support, there are people who rebuild phonograph transducers and other subassemblies. Availability of specific spares depends on several things. OEM spares support for pre-1930's items was discontinued before WW-II, but in many cases, items of new manufacture are available. In other cases, such as the 6U5/6G5 tuning eye tube, commonly used from the '30's to the '50's, your best bet is to substitute (and there is an adaptor for this available). Q. I've never worked on vacuum tube equipment before, but I'm a ham and I have worked on lots of transistor equipment and small computers. Can I just jump in and fix my old radio? A. No. There are some serious differences between old tube equipment and modern solid state electronics. Here are a few things to consider: a. DANGER! HIGH VOLTAGE! We are not talking about 110 volts AC, we are talking about 250-500 volts with plenty of "oomph" behind it. You generally won't find any fuses in old electronic equipment, and no protective circuits. b. Vacuum tube circuits have components and circuitry that isn't used in solid state equipment. While the basics of physics regarding voltage, current, resistance, inductance, and capacitance haven't changed, you'll want to study old texts that explain the theory of operation of the circuits used. While developing the skills needed to trouble-shoot and repair vacuum tube circuits is not difficult, it is very different work from working on solid state equipment. And, as noted, the presence of genuinely high voltages for someone used to working with 5 and 12 volts means that you will need to develop new safe working habits. Q. I'm all thumbs around mechanical and electronics devices. Can I find people who know how to make these things work? A. Yes. You may find someone locally who still does work on tube electronic equipment, and a few telephone calls to service shops will point you in the right direction if there is someone in your area. There are a few people who specialize in repairing and restoring old phonographs and old radios. While none are listed in this revision of the FAQ, we may include a few if there is a demand for this information. For a price, you can have almost any antique "high-tech" device restored to like-new condition, if not better. Q. What is a "boatanchor." A. This is a ham radio term for old receivers, transmitters, and test equipment, primarily vacuum tube devices. There is a "boatanchor" mailing list; however, the maintainer has been offline for several months and subscription requests are presently not being honored. (This item will be changed when the maintainer becomes active again). The address of the mail list is boatanchors@gnu.ai.mit.edu. -- *********************************************************** Hank van Cleef vancleef@bga.com vancleef@tmn.com *********************************************************** From vancleef@bga.com Thu Dec 15 02:20:10 EST 1994 From: vancleef@bga.com (Henry van Cleef) Subject: FAQ rec.antiques.radio+phone (part 2 of 5) Date: 14 Dec 1994 01:26:02 -0600 Lines: 273 Message-ID: <3cm6ma$1r3@ivy.bga.com> Summary: Part 2 - General questions about acoustical phonographs. 1.0 Oct. 20, 94 First version. This material was supplied by George Conklin (george@nccu.edu). 1.1 Dec. 12, 94 Revisions by George Conklin. Part 2 - Frequently-asked questions about phonographs ------------------------------------------------------------------------------ FAQ editor: Hank van Cleef. Email vancleef@bga.com, vancleef@tmn.com This is a regular posting of frequently-asked questions (FAQ) about antique radios and phonographs. It is intended to summarize some common questions on old home entertainment audio equipment and provide answers to these questions. The most frequently asked question so far is "Where can I buy steel needles for my Victrola?" Answer: Contact the Antique Phonograph Supply Company, Route 23, Box 123, Davenport Center, NY 13751. Phone 607-278-6218. Remember to change your needles after every play. The engineering concept was simple: the needles are softer than the record, and will wear without stressing the record. Some records had grit in the mix to wear the steel needle. Question: My phonograph does not work. What can I do? Answer: There is one excellent book which explains how old phonographs, gramophones and cylinder players work. "The Compleat Talking Machine" by Eric Reiss. It is also available from APSCO listed above. It explains how to work on a phonograph to get it running again. It contains detailed photographs. Question: I have just found this wonderful windup phonograph. How can I tell if it works? I don't have time to read a book. What can I do? Answer: Phonographs are found which look new. Others look as if they have been sitting in a wet basement for 70 years. But there are a few quick tests: 1. Does the dealer demonstrate the unit? If it plays and sounds fine, it probably is in good shape. It is relatively hard to hide problems with spring motors. 2. Is the spring broken? This means that your turn the crank and nothing happens. Usually the spring is broken near the center, so the phonograph does not play. New springs can be found for most phonographs from the Antique Phonograph Supply Company. Cost: about $50 if you send in the barrel. 3. If the turntable rotates (or the cylinder turns), but you hear a loud bump while the record is playing, then the spring needs grease. a. This is not an easy task. Purists will say to take the spring out of the barrel, clean it and the reload the barrel. Warning: if you try to do this, you can cut your fingers off. The barrel is a cylinder into which the spring is wound. Some cheaper units simply have an open spring. Greasing such a spring is much more easy. b. Shortcut: You can add grease to the spring without first taking it out of the barrel. Most barrels had an opening called a graphite hole. Wind up the unit all the way. Take the plug out of the graphite hole and force in grease. The original Edison formula, which I have used, contains 10 parts vasoline to 1 part graphite. Put the screw back in the hole. Let the unit run down, dispersing the grease. 4. Listen to see if the governor is in good shape. When you play the unit, is there a high speed vibration. If so, you may need work on the governor. This is difficult. 5. If the turntable works (or the cylinder turns), then play a record. What does it sound like? If you hear a lot of vibrations, or if the sound is bad, you probably need to rebuild the reproducer. a. Rebuilding an Edison reproducer for a cylinder phonograph is ususally an easy job. Kits cost $6.00. A new sapphire is $30.00 and is likely to outlast you. b. Rebuilding a Victor #2 (the most common) is not difficult either. c. Rebuilding a Diamond Disc reproducer is more difficult. The old diaphragms take effort to remove without damage. It can be done. Kits are available. New diamond needles: $60.00. But the old diamond may be in good shape. d. Rebuilding the Victor Orthophonic is very difficult and few people will touch this one. Such reproducers (heads) cost about $100 in auctions. Many were made of pot metal, and they are gradually falling apart. e. Rebuilding other heads requires buying generic parts and doing the best you can. 6. Ok, I don't know much about mechanical things. What can I do? You can send the entire works off for repair and cleaning. This costs about $150 for an Edison unit. 7. What about parts? What if something wears out? If you buy an Edison or a Victor, most motor parts are still available. As for the other units around, if something other than the spring is broken, you might want to look for a different unit unless you are handy around a machine shop, or are willing to pay to send the entire motor out for repair. Question: I just found some 'thick' records. How can I play them? Answer: Many people think that the standard 78 record is 'thick.' However, the really thick records were made by Thomas Edison and are called Diamond Discs. They were made from 1912 until Edison closed his phonograph business in 1929, one day before the stock market crashed. In their time, these were the premium records. Do NOT try to play a diamond disc record with a Victrola steel needle machine. It will ruin the record and it will not play. The DDs were recorded vertically, using the hill and dale method. They were played with a special diamond needle. You can play such records today at 78 rpm on with a stereo catridge using either the LP needle or a 78 (3 mil) needle. Or, better yet, such records still work fine with an Edison machine. Question: I just found a "Victrola." What is it worth? Answer: Most people use the word 'Victrola' as a generic term, like Frigidaire is used to mean all types of ice box. Most likely such a term means an upright machine made during the 1920s and housed in a 'brown box.' Since millions were made, it is impossible to give a specific value. However, most upright Victors go for about $400 right now. Question: Where can I read about my Victrola? Answer: Buy the book "Look for the Dog" by Robert Baumbach. It lists all Victor models, starting with the open horn machines. Some were quite rare; most very common. Production figures are given. Buy the book from Allen Koenigsberg, 502 E. 17th Street, Brooklyn, NY 11226. Phone 718-941-6835. Question: Where can I find out about record auctions? Parts? Supplies for old phonographs? Answer: Join MAPS, the Michigan Antique Phonograph Society, 2609 Devonshire, Lansing, MI 48910. Phone John Whitacre at 517-482-7990. After you join, purchase the Resource Directory. It lists hundreds of dealers and places to buy records and get your phonograph serviced. It also lists other clubs. Question: I want to buy an Edison Standard. Can you name some dealers in my area? Generally the answer to this question is unfortunately 'no.' The market for used phonographs remains fragmented. In certain areas there are well-known dealers. But you are not going to find one listed in every city. Antique malls often sell machines that are offered to them. Prices can be high. Question: I just found a phonograph. I can't remember the name. Who made old phonographs anyway? Answer: The phonograph was invented by Thomas Edison. He let it sit on the shelf for 10 years. His patents covered cylinder records, the original format. Later Berliner obtained a patent for what we call today the 78. Its virtue was that the 78 could be mass produced easily. Victor took up the Berliner patent. Edison stayed with cylinder records. By 1920 it seems as if every furniture store would put together a case and generic works and a new brand was born. Sometimes Edison would sell spare cases so conversion companies would put together parts from different sources even in well-known cases. Some common brands: Edison, Victor, Sonora, Brunswick, Silvertone, Zonophone, Aeolian, Pathe, Granby, Columbia, Vocalian, Harmonola, Heinman and others. Question: Where can I learn about the history of the phonograph? Answer: write to Allen Koenigsberg, 502 E. 17th Street, Brooklyn, NY 11226. Request a collectors check list. Most important books can be purchased through him. The most scholarly is "From Tinfoil to Stereo, 1877-1929" by Welch and Burt. Unfortunately, the authors concentrate on the legal fights faced by early phonograph producers, and not the technological problems the had to overcome to bring talking machines to market successfully. Koenigsberg also publishes the "Antique Phonograph Monthly." It contains interesting articles about phonographs. Be warned: it comes out every year or so, not monthly. Since the history of phonographs is a hobby not a scholarly undertaking, people do this sort of thing in their spare time. Question: What is a gramophone? Answer: The British refer to a phonograph which plays flat records as a gramophone. In British usage, a phonograph plays cylinders only. Question: I just found an Edison cylinder player. Where can I find out about how it works? Answer: There is one authority on Edison players, both cylinder and the Diamond Disc (DD) type. His name is George Frow. He wrote two books which define the field. The book on cylinder phonographs is just about to be republished in a new edition called "Edison Cylinder Phonograph Companion, 1877-1929." Available from several sources, but I have a listing from Koenigsberg listed above. It is due out in November 1994, but may be delayed. The second book covers Edison Diamond Disc machines. "Edison Diamond Disc Phonographs, 1912-1929." Frow covers all models, including some which may have never been made! His research comes from the Edison historical site in Orange, NJ. Source: write Frow himself at George Frow, "Salterns" Seal Hollow Road, Sevenoaks, Kent, TN13 3SH England. He airmails the book, with no delay. Check for current price. He took my personal check. Also available from Koenigsberg listed above. Question: Where can I find a list of cylinders which were made? Answer: Wax cylinders made up until by Edison 1912 are covered in a book written by Alan Koenigsberg, 502 E. 17th Street, Brooklyn, NY 11226. Celluloid cylinders made by Edison are listed in a publication sold by The City of London Phonograph and Gramophone Society (CLPGS), Mr. Chris Hamilton, "Ardlarich," 2 Kirklands Park, Cupar, Fife KY15 4EP, Scotland. Phone: 44 334 543 90. Question: Are there any magazines which discuss old phonographs? Yes: Personally, the most interesting is Hillandale News published by CLPGS listed above. It is a glossy magazine well produced. It contains about 40 pages per issue. Also, the Michigan Antique Phonograph Society has a monthy newsletter which answers questions from readers. Question: What are the most common old phonographs? Answer: The phonographs which have survived today are Edison, Victor and Columbia. Of the three, Edison was the most sturdy, although Victor was often well made also. The Columbia units used more pot metal, which decays with age. Question: Are all phonograph cyliders the same? Answer: Not all phonograph cylinders are the same. The cylinder was the original format for recording. The most commonly found ones today are Edison's black wax (Gold Moulded) cylinders. These play for 2 minutes. Columbia made 2-minute cylinders out of celluloid. Such cylinders last a long time. Later everyone switched to 4-minute cylinders. Edison always offered kits to upgrade his players. The 4-minute cylinders turned at 160RPM (as did most 2-minute cylinders) and had 200 grooves per inch. Edison produced 4-minute wax cylinders and later 4-minute blue celluloid cylinders. The blue cylinders (called Blue Amberols) were launched in 1912 and were made until 1929, long after everyone else quit making them. I have just found a phonograph in a brown case. When as it made? If the phonograph has a large external horn, it was made before about 1912. After that, the ladies wanted horns inside a case, hidden from view. If the unit you are looking at has an enclosed soundbox in a pice of furniture, it was made >from 1910 or so up until the end of the wind up era about 1930. Not many phonographs were made from 1929-1945. The depression caused a collapse of sales, with one authority claiming that record sales declined by 90% during the 1930s. Question: What is the difference between Victor and Victrola? Answer: The Victor Talking Mahince Company made external horn phonographs. When they switched to horns inside of the case, the name -ola was added. Victrola technically means an internal horn machine. Edison did the same thing. He called his internal horn cylinder machines Amberolas. Question: I have some 78s I got from my family. I am afraid of hurting them with a diamond needle. How can I play such records? You can play 78s with a modern phonograph using a diamond needle. If you have only a stereo stylus, you can still use it to play your 78s without hurting them. Of course, it is best to use about a 3 mil needle made for the purpose. Modern equipment, tracking at 2 grams, is quite gentle on records compared to the old Victors, tracking at several ounces. -- *********************************************************** Hank van Cleef vancleef@bga.com vancleef@tmn.com *********************************************************** From vancleef@bga.com Fri Dec 16 10:21:05 EST 1994 From: vancleef@bga.com (Henry van Cleef) Subject: FAQ rec.antiques.radio+phone (part 3 of 5) Date: 16 Dec 1994 02:11:45 -0600 Lines: 747 Message-ID: <3cri41$fua@lia.bga.com> Summary: Part 3 - General questions about vacuum tube radios and phonos. Rec.antiques.radio+phono Frequently Asked Questions (Part 3) Revision Date Notes 1.1 Oct 24, 94 Was part 2, now part 3. New material and revisions. 1.2 Dec. 5, 94 Added references to RCA Receiving Tube Manual, corrections and new material. Part 3 - General questions about vacuum tube radios and phonos. ------------------------------------------------------------------------------ FAQ editor: Hank van Cleef. Email vancleef@bga.com, vancleef@tmn.com This is a regular posting of frequently-asked questions (FAQ) about antique radios and electronic phonographs. It is intended to summarize some common questions on old home entertainment audio equipment and provide answers to these questions. Q. What is published to tell me what an old radio is worth? A. There are some guides that list prices. The most commonly mentioned is Bunis, Marty and Sue, "The Collector's Guide to Antique Radios." It is available from Antique Electronic Supply. There are several other books available from them for identifying old radios, some with price information. What a specific radio actually is worth may be quite different than what these guides list. In addition, the condition of the radio (both cosmetics and electronics) has to be considered. Q. I just got an old radio at a yard sale for $5. It is a Radio Wire Television Model J5. When was this radio built? Can I get it to work? Is this radio worth restoring? Can I get a schematic somewhere. A. Requests like this send everyone scrambling for their references, schematics manuals, etc. etc., and sometimes nobody responds. There is some very basic information that you could, and should, include, that would get you an answer instantly. If you included "this radio uses five tubes. They are 12SA7, 12SK7, 12SQ7, 50L6, and 35Z5." See below on "how to date radios by design features." Listing the tubes often says everything. The example used here is one of an endless long list of AC-DC table radios built after 1940 using this tube complement. Most people who repaired radios in the forties and fifties could draw the schematic for any of these radios from memory----it's a case of "seen one, seen 'em all." This particular radio has a grand total of 9 resistors (including volume control), a whopping 14 condensers (including the tuning condenser as one), three transformers, one oscillator coil, a loop antenna, a loudspeaker, and a panel lamp. Add the five tubes, and that amounts to the whopping sum total of 35 electrical components, and if you want to insist on including the chassis, five tube sockets, cabinet, panel lamp socket, and cabinet, we are still talking about 50 parts. No wonder they sold for $4.98 in 1940. If it has value, it is for its case and mechanical configuration. As a project radio to learn radio repair and restoration, an AC-DC 5 or 6 tube table set is probably ideal. Most of these sets need one tube (burned-out heater), new electrolytics and paper capacitors to get it "working like new." Q. I just looked at a Radio Wire Television model B45. It has 13 tubes and two loudspeakers. I couldn't see all the tubes but I saw a 6H6, two 6L6's, two 5Y3's, and a bunch of metal tubes with top caps. It has three bands, two shortwave, and a phono, and is in a custom-built plywood cabinet. What can anyone tell me about this set. The radio works, but not well. The owner wants $100 for it. Is it worth it? A. This is the type of radio you should be asking questions about. The radio itself is a "class act"---high fidelity, 1938 style. It's the same manufacturer listed in the question above, and shows that "brands" could range from absurdly cheap to top quality. It also is typical of the radios that justified service shops paying good money for Rider's manuals over the years. As a "collector" radio, it's a difficult one to put dollar value on. But as a museum piece, an example of what a high-end thirties radio was, it is a class act. For those who have Rider XVIII, look at Radio Wire page 18-8, and notice that only the schematic and a few notes are published, some ten years after the radio was made. (confession: I owned one of these from about 1948 until sometime in the sixties, and it was my first really hard-core restoration project. It also was my "hi-fi amplifier" for many years). If you want an example of high tech history, it's well worth the $100, and if you restore it, you'll find that quality is a lasting thing. But restoring a set like this can be a major project and take a good deal of skill. Other "high tech" radios that are more readily identifiable by brand name are the Farnsworth Capehart sets and the 2-chassis Magnavoxes. Q. I saw a little table radio with a very pretty plastic case, but the owner want hundreds of dollars for it. The case looks like marble, but the radio inside is just another of those 35Z5 and 50L6 five tube jobs. Why does the owner think its worth almost a thousand bucks? A. Well, you've stumbled on the collectors' hot item of the nineties, the "Catalin" case. The reason the owner thinks it is worth this much is that the collectors' market seems to be willing to pay these prices for a catalin case. Whether it will continue to do so is open to question. It is difficult, in a FAQ item, to explain the whimsies of the "collector" market, because these tend to change. Q. Well, if a low-tech radio is worth hundreds of dollars because of its case, and a high-end console with tremendous sensitivity and a powerful amplifier with good fidelity is worth a lot less, what's the correlation between price and value? A. There isn't any. Some radios, such as the Atwater Kent TRF sets and the RCA catacombs superhets are valuable because they are relatively rare today, and represent technological history. An old communications receiver, such as the Hallicrafters SX43, which was also sold as a home entertainment radio, has much more value to a ham than an old Magnavox radio-phono, so has value because of its technology. Novelty items, particularly if they are rare, seem to be high-ticket "collectibles" in any area. So you see dollar values attached to radios with reading lights built in, radios with cameras in them, catalin cases, the Sparton blue mirror sets, incredibly small portables, etc. Q. I keep hearing about "Neutrodyne," "TRF," and "Superheterodyne." What do these terms mean? A. The first home entertainment radios were crystal sets which used a single tuned antenna circuit and a crystal detector. When tubes were added for amplification, these were set up with tuned circuits that had to be individually tuned to the station being received. These are "TRF" sets, for "tuned radio frequency." Later on, manufacturers learned how to build TRF stages using either mechanical coupling between the tuning condensors or a single ganged condenser, and to provide adjustments to get them to track (i.e., all tune to the same frequency across the range of broadcast frequencies), so later TRF sets have one-knob tuning. The Neutrodyne refers to a method of "neutralizing," or compensating for, detuning effect of grid-plate capacitances by feeding back an opposing signal. These sets are TRF sets with neutralizing circuits in them---generally, another coil in the tuned circuit used to generate the neutralizing signal. The superheterodyne uses the physical principle that two oscillators running at different frequencies will produce "beat" frequencies equal to both the sum of and difference between the two frequencies. This can be heard when tuning musical instruments; the principle is the same for radio frequencies. The incoming RF signal is "mixed" with a local oscillator signal and fed to a fixed tuned stage that is sensitive to the difference frequency between the two signals. Use of one or more fixed-frequency tuned stages gives the set relatively constant sensitivity and selectivity, both of which are difficult to get in variable tuned stages. To illustrate what these words mean, take a common five-tube US table radio and a station at 1000 Khz ( 1 megacycle). An antenna coil and one section of the tuning condenser (capacitor) are tuned to resonate at 1000 Khz, "selecting" that frequency. A local oscillator is tuned by the other section of the tuning condenser to 1455 Khz. In a set with a 12SA7 tube, the 12SA7 is wired as an oscillator, with the oscillator signal appearing on the first grid (g1). The tuned RF signal is fed to the third grid (G3). The plate circuit is connected to a transformer tuned to 455 Khz, to respond to the difference between the frequencies being injected on G1 and G3. Signals at 455, 1000, 1455, and 1455 Khz all appear on the 12SA7 plate (the two fundamentals and the sum and difference), but the tuned "intermediate frequency" (IF) transformer selects only the 455 khz signal. This intermediate frequency is generally amplified by one or more tuned (455 khz) stages---in our example, a 12SK7 with double-tuned input and output IF transformers (i.e., both the plate and grid circuits are tuned to resonate at 455 Khz) is used, and the output of that stage is fed to the a diode detector. This may sound a bit complicated, and I've left out all the fine points of the design to focus on "what's supposed to happen."---a good engineering text discusses design details beyond this description. One point of terminology----the mixer stage (12SA7) was often called a "first detector" in early designs; thus, the 12SQ7 diode detector in our example is called the "second detector," a term that has persisted through the decades. One other common early design was the "regenerative" set. In these sets, an RF amplifier was designed as an oscillator, but provided with a control that could be adjusted so that the stage wouldn't go into oscillation. The positive feedback in the stage provided substantially more gain than a simple tuned circuit would provide. Misadjustment of the feedback control would make the stage oscillate, producing squeals in the output, and quite powerful RFI (radio frequency interference) as well. The "superregenerative" circuit is a refinement that prevents sustained oscillation, but was generally not used in home entertainment sets. Q. I have an old radio-phono. The radio works fine, but the phono doesn't make any sound in the loudspeaker at all. What's the deal? A. Your phono pickup probably uses a Rochelle salt crystal cartridge, and the salt crystal has failed. You will need a new cartridge. (faq editor note---I'm including this, and have a radio-phono with a dead cartridge. What's available?). Q. I just got an old radio that I think was made in 1939. But it has a jack on the back labelled "television." It only has a volume control/on-off switch and tuning control on the front. What's the deal with the jack? How can a radio receive television, and why is a 1939 radio labelled like this when TV broadcasting didn't really begin until after the war. A. You are looking at a marketing ploy. The jack on the back is an audio input jack, and if there is no switch for it, it is wired permanently to the top of the volume control (detector output), so has whatever signal the radio is receiving on it as well. Television was "just around the corner" in the 1937-39 period and there were some experimental stations broadcasting what is essentially NTSC video on Channel 1 (48-54 Mhz) after 1936. Putting these jacks on the radios was to convince the buying public that their new radio wouldn't be made obsolete by television "next year." Commercial television actually began in 1939, but WW II intervened, and the mass-marketing push for TV did not begin until 1946-7. Q. I have a console with 6L6's and a twelve-inch loudspeaker. Is this "high fidelity?" Just what can I expect to hear from my old radio for audio quality? A. (revised 12-94) (This item originally indicated that bandwidth was limited to 50 cycles to 5 Kc by program sources, which provoked considerable discussion in the newsgroup). Based on measurements on a 1949 Magnavox AM-FM-SW-phono (3-speed) console with 4 speakers, it is unlikely that any of the packaged high-end consoles had sufficient bandpass to be called "high fidelity" in any modern term. What you will get from one of these sets is hum-free low-distortion audio that makes very pleasant listening. A good floor console or cathedral radio, operating properly, should have good-quality audio for AM broadcast listening. Q. I have a nice old Philco cathedral radio that I have listened to for years. It only gets local stations, and even at maximum volume, is not particularly loud. Can I get it to work better than it does now? A. Probably. You have a sixty-year-old piece of electronic equipment that has probably had two or three tubes replaced, and maybe one bad capacitor, in those sixty years. In short, it's a candidate for an electronic overhaul. Some things that may have degraded over the years: a. Capacitors. Electrolytic capacitor problems generally make themselves known quite quickly. However, those little wax-impregnated "paper condensors" may all be leaking current and delivering less capacitance than needed for good performance. b. Resistors. These may have "drifted" to a much higher resistance gradually. c. Misalignment of tuned circuits. The "tweaks" on the tuning condenser and the IF transformers generally don't drift very far unless the coils have absorbed moisture. Altogether too often, the amateur restorer will tweak the set out of alignment by fiddling with these. Don't touch them unless you know exactly what you are doing and have the equipment needed to align the radio. d. Tired tubes. I put this last, although a lot of people look here first, and assume that a tube tester's readings will correlate with set performance. The best test for tube condition is to substitute a known good tube in each position and seeing if it changes anything. A sick pentagrid converter tube (6A7, 6A8, 6K8, 6SA7, etc.) may very well test normally under DC conditions in a tube tester yet fail to oscillate reliably in the set, particularly on shortwave. Q. You say "electronic overhaul." Will that restore my set to like-new performance? A. Generally, yes---actually, better than new. Modern resistors and capacitors are better circuit components than were available in the thirties and forties. Capacitors in particular are much smaller, and larger values can be used to advantage in some places, particularly in the filtering circuits. Q. Modern components? But if I put modern components like mylar capacitors in the set, it won't be "original" any more. A. There is a wide range of opinion about use of modern resistors, capacitors, and wire in an old radio. Some feel that disguising modern components in the shells of old wax paper capacitors is important. There are (at least so far as your FAQ editor knows) no clear-cut guidelines on the "looks" of components installed under a radio chassis. Consensus seems to agree that all items that are visible when the chassis is bolted in place should "look like the original radio did." Q. I have a Philco battery-powered radio. It has a four-prong plug for the battery. Can I get a converter at Radio Shack and use it to make my radio work? A. No. The battery radios required 1.5 volts for the tube filaments and 67-1/2 or 90 volts for "B" (plate) voltage. The 3-way portables (AC-DC-battery) had built-in battery eliminators, and the tube filaments were generally wired in series, requiring a 6 or 9 volt "A" battery. You'll need to make a supply that can deliver 1.5 volts at about 400 ma. and 90 volts at about 50 ma. for your four-prong Philco. Both have to be good clean filtered DC. The power-pak-in-the-plug type power units sold by Radio Shack and others are made to deliver 6-9 volts at 100-200 ma. unfiltered DC. DATING OLD RADIOS BY THEIR TUBE COMPLEMENT The development of vacuum tubes, both electrically and mechanically, advanced at a rapid pace between about 1925 and 1950. The vast majority of radios sold for home entertainment between 1920 and the late 1950's were built to various standard circuits. In most cases, checking out what tubes are used in the radio will place it's date of manufacture within a few years, identify which of the standard circuits it used, and give a some indication of the quality of the set. Most radio repair technicians in the 1930-60 era did not need to look at schematics most of the time, even when the problem was not a burned-out vacuum tube heater or filament. The tube complement is not always an accurate guide, except insofar as the presence of a given tube indicates that the set was built after that tube was placed in production. You won't find any 1932 radios using tubes with octal bases or 6.3 volt filament heaters, and you won't find any prewar radios with 7-pin miniature tubes. But you may find a 1946 table radio built to a 1935 design. There are also a few other design features that are very obvious on casual inspection; I'll mention some of them as we go along. (New 12-94) In the following discussion, there are references to the example circuits shown in the RCA Receiving Tube Manual RC-19, dated 1959. This manual is available in reprint from Antique Electronic Supply. Examples 19-1 through 19-4 in particular show examples of four standard circuits that were used, either identically or with minor modifications, in the majority of the smaller "collectible" radios built >from the mid-1930's on. 1. The five or six-tube AC-DC radio with 150 ma. tube heaters wired in series. Example circuit 19-4 shows one of these radios, using 7-pin miniature tubes. This design is colloquially called the "All-American Five" by some of us. The design was first built in 1939, using octal tubes (i.e., 35Z5 and 50L6 in place of 35W4 and 50C5), so it is also called by some a "35Z5 radio" or a "50L6 radio." I list this design first, not only because it dominated home entertainment radio production for over 20 years, but because it is a very simple superheterodyne circuit. If you study this circuit and know what every component's function is, and study an example radio of this design, you'll be prepared to trouble-shoot and repair most post-1935 radios. These sets do not have a power transformer, and could operate in places like mid-Manhattan, which had 110 volts DC as its primary electrical service. Most of these were built as table radios, although some were installed in small consoles and radio-phonograph combinations. Virtually all clock radios use this circuit. These are generally AM-broadcast-only. The tube set shown in the example is one of three common sets, having either octal, loctal, or 7-pin mechanical design, but electrically equivalent. Some sets, particularly in the early postwar period, were built with mixtures of tube mechanical types, because of tube shortages and availability, and some sets used more than one configuration during their production runs. The six-tube version had an RF preamplifier, and was more sensitive than the five-tube. Example circuit 19-3 shows the same basic design with an RF preamplifier stage, with tuned output (three-section tuning capacitor). Many of the six-tube versions used resistance coupling between the RF preamplifier and the converter stage (see Diagram no. 3, p. 339, in RC-19, for a resistance-coupled pentode circuit). The six-tube version was often called a "35L6 radio" because a 35L6, 35A5, or 35C5 was used, allowing connection of one more 12-volt heater in the series heater string. In the fifties, some of these radios were built with a selenium rectifier, omitting the rectifier tube. Also, a few manufacturers built a four-tube version that omitted any IF amplification. Several low-end "boatanchor" communications sets used this circuit, adding multiple tuning coils and provisions for a beat-frequency oscillator. Notable examples are the Hallicrafters S-38, S-41, S-119, S-120, and Ecophone EC-1 series; and the National NC-46 and SW-54. The tube complements are: a. First version, built primarily 1938-40. (note: this design is similar to the 19-4 example, but is its immediate prececessor, so has a few substantial differences, noted below). 12A8 RF-converter, 12K7 IF amplifier, 12Q7 detector-audio, 35L6 power output, and 35Z5 rectifier. The first three tubes had small top caps for the signal grid connections, with either metal or glass envelopes. The original glass tubes had a "G" suffix, indicating use of an ST-12 stepped bulb envelope. The major difference between this design and that shown in example 19-4 is the use of a 6A8, which uses a slightly different oscillator circuit than the 6SA7, 14Q7, or 6BE6. The other top-cap tubes are very similar to the single-ended octal tubes which followed, varying primarily in mechanical construction. 6J8 and 6K8 were sometimes used as converters as well. RC-19 unfortunately omits any circuits for these converter tubes. This version uses a series resistor in the heater circuit because the heater voltages do not add up to "near 120). The proper place for this resistor, electrically, is between the rectifier heater and the power amplifier heater. b. Second version, built 1939-ca. 1960 (Note from FAQ editor---the original FAQ specified 1940 as the year of introduction for single-ended octal tubes. Typically, they were introduced in "1940 models," but were built beginning in 1939). 12SA7 RF-converter, 12SK7 IF amplifier, 12SQ7 detector-audio, 50L6 power output, 35Z5 rectifier. This is almost the same radio, but using single-ended tubes in the first three stages and a power output tube with a 50-volt heater. The major difference is in use of a 12SA7 in place of the 12A8---these tubes are different internally. Note that the sum of the nominal heater voltages adds up to 122.8 volts, allowing operation without need for any series resistor in the heater circuit. c. Postwar version, 1945-mid '60's 12BE6 RF-converter, 12BA6 IF amplifier, 12AT6 detector-audio, 50B5 power output, 35W4 rectifier. The only difference here is the use of seven-pin miniature tubes. All are electrically identical to the octal versions above. Some sets were built using a mix of seven-pin miniature and octal tubes, however, the presence of seven-pin miniature tubes indicates that the set is postwar production. d. Loctal tube version, 1940-ca. 1960 14Q7 RF-converter, 14A7 IF, 14X7 detector-audio, 50C5 power output, 35Y4 rectifier. Once again, the same radio as version b., using loctal-base tubes in place of octal. Philco and GE were fond of using loctal tubes. Note that some radios used a 14B8 converter, which is the same configuration in a circuit as the 12A8. The six-tube configuration used the same tube type for both RF preamplifier and IF amplifier, and the 35 volt heater version of the output tube. In most cases the RF preamplifier is resistance-coupled to the RF-converter stage, and the radio used a two-stage tuning capacitor. Some later versions used movable slug tuning in place of a variable capacitor. This variation began around 1947, and became more common during the next decade. 2. Five or six tube AC-DC transformerless radios using 300 ma heaters wired in series. These radios were the precursors of the 150 ma. series heater radios. Some of these radios also included a tuning eye indicator, typically a 6E5. Total voltage drop of the series heater string was 68-74-82 volts requiring an external voltage dropping resistor of some sort. These radios often used "ballast" tubes or resistance wire in the line cord for this purpose. a. Version using large-base 5, 6, or 7-pin tubes, 1935-50. 6A7 RF-converter, 78 or 6D6 IF, 75 detector-audio, 43 power output, 25Z5 rectifier. Most of these sets were built before 1938, although a few manufacturers built them in the early postwar era. There are more variations on this design than on the 150 ma. heater designs described above. As noted, some sets had 6E5 tuning eye tubes. Sets with shortwave often had a 76 triode as a separate local oscillator for the 6A7. b. Version using top-cap octal tubes, 1936-1950's. 6A8 RF-converter, 6K7 IF, 6Q7 detector-audio, 25A6 or 25L6 audio, 25Z6 rectifier. This reflects the switch to octal tubes in 1936. The first three tubes had small top caps for signal grid connection. The 25A6 is an octal version of the 43; the 25L6 is a 25 volt heater beam power tube identical, except for heater, to the 35L6 and 50L6. The 25Z5 is a full-wave rectifier (two diode sections), and was usually connected with the two sections in parallel. However, some manufacturers, notably Philco, used the two sections to provide voltage doubling for B+. Radios with voltage doubler power supplies are AC-only, as a voltage doubler requires alternating current to "pump" the doubler circuit. c. Version using single-ended octal tubes, 1939-50's. 6SA7 RF-converter, 6SK7 IF, 6SQ7 detector-audio, 25L6 output, 25Z6 rectifier. Once again, this is a "switch," this time to single-ended octal tubes. Major circuit difference is in the 6SA7 circuit because of differences internally between the 6SA7 and 6A8. This version was generally not built as a "price leader" inexpensive table radio because of the availabity of 150 ma. tubes that didn't require a dropping resistor in the heater circuit. It was very often used as the basis for an upscale AC-DC radio. Some configurations that you may run across: 1. Shortwave receiver using an additional RF preamplifier, separate local oscillator, and second IF stage. The 6SK7 was used for the RF and IF stages, and a 6J5 as a local oscillator. 2. Push-pull audio output, using two 25L6 tubes and a 6J5 as a phase inverter. This may be combined with the RF-IF additions, above, and a tuning eye tube (6E5 usually). Note that use of rectified line voltage gives a relatively low B+, a major limitation in the transformerless design. The primary market for a "full house" receiver that had all of these features would have been the DC service metropolitan areas, particularly New York City, and that is the general area where most "odd-ball" configurations of transformerless sets can be found today. In summary, all of the designs identified in items 1 and 2 above either used the circuit shown in RC-19 example 19-4, or fairly simple variations of the design. There are very few radios with these tube complements that vary markedly from the design, which was established around 1932, and licensed to builders through Hazeltine and RCA patent licenses. In general, the sets that deviate markedly from the standard circuit are a few Philcos and Zeniths, and some off-brand sets that may have been marketed through chain stores with chain store brand names. 3. Postwar AM-FM sets, 1945-up. These were made in two configurations: separate FM front end, and common front end (i.e, RF, IF, mixer, and IF amplifiers. There are many variations on both designs, using 7-pin miniature tubes, loctal tubes, or "hot" octal tubes. The 6SB7Y was a "hot" 6SA7-type tube capable of self-exciting oscillation at FM frequencies, and the 6SG7 a "hot" replacement for the 6SK7. The presence of 88-108 MC FM in a radio always means that it is a postwar set, as this band was not assigned to FM until April, 1945. Manual RC-19 shows an example of an FM tuner in example 19-9. Many AM-FM sets "merged" AM capability into the FM tuner design by using a bandswitch in the RF and converter stages, and by connecting IF transformer coils for 455KC and 10.7 Mc. in series, the idea being that the desired frequency will cause one or the other to resonate (high impedance) and the other will appear as a low DC resistance. The bandswich would also select which IF fed the AM detector, and which detector's output was used to feed the audio section. Example 19-9 also shows both the limiter-discriminator and the ratio detector designs commonly used in FM-capable sets. This ends the "most common" AC-DC section. Now we will consider history, and some of the other designs. Example 19-1 in RC-19 shows a later battery-operated portable, using 7-pin miniature tubes. This design was built after about 1934, originally using 5-6 pin tubes in ST-12 bulbs; later, octal or loctal tubes. This circuit also is the basis for most later battery-operated "farm" sets, some of which were built as floor consoles. Close study of the circuit will show its resemblance to the 19-4 example. A very significant difference is the use of filament tubes, and the method of using a back-bias resistor (R10 in the example) to develop grid bias voltage for the output tube. Note also that a different local oscillator circuit is used for the 1R5. This circuit was often used in the "All American Five" design as well, and is not unique to the battery design. Resistance values in example 19-1 have been chosen for operating with a 67.5 volt B battery; otherwise, the circuit is suitable for operating with a 90 volt B battery. Example 19-2 shows a typical three-way portable. The term "three-way" may seem confusing, when the radio can be operated either from the power line or from batteries. However, the fact that it could operated from 110 volts DC as well as from AC lines was considered noteworthy when DC domestic service was common; thus "AC or DC or internal battery" are the "three ways." Note that a modern ricebox radio operating on an internal battery or with an AC adapter is not "three way" as it will not operate >from a DC line. Once again, this is the Hazeltine-RCA standard circuit used in examples 19-1 through 19-5, with specific provisions for the three way feature. Example 19-2 also shows use of a double-tuned RF preamplifier. Notable are the use of series connection of the receiver filaments, provision of a rectifier, and a changeover switch. In practise, many manufacturers provided a dummy line-cord outlet inside the receiver. Plugging the line cord into this outlet would mechanically actuate the changeover switch, placing the receiver on battery operation. When studying this circuit, note in particular the order in which the tube filaments are wired, and the use of an 1800-ohm resistor (R14) in the 3V4 filament circuit to provide a shunt-feed balance current. The order of connection of series-wired heaters and filaments is significant in series-string sets. In this case, the 3V4 is connected to the high end to provide grid bias for operating, and the shunt resistor provides some of the plate and screen currents for the tube. The rectifier circuit shown is typical, although three way portables may use a 35Z5 or a selenium rectifier. DC output from the rectifier is around 120 volts, depending on the rectifier used, which requires a large dropping resistor to feed the receiver filaments. Note the use of two large electrolytic filter capacitors, C28 and C29, connected to either end of the 3V4 filament. Small filament tubes require "clean" DC power, thus these two capacitors filter out both residual ripple from the half-wave rectifier and audio-frequency variations caused by varying power draw of the power tube. This circuit arrangement is critical. If any filament opens, one or both of those capacitors will charge up to the rectifier output voltage. Also, the design assumes that the rectifier is part of the voltage-dropping string, and 1.5V filament tubes are limited in their ability to handle out-of-tolerance filament voltage. The circuit shown in figure 19-3 for an AC-operated receiver is the same as that in figure 19-4, with several upscale features, and resistance values selected for operation at 250 volts B+ rather than 120. Note that the circuits for the 6BE6 converter, 6BA6 IF, and 6AV6 detector-audio stages have the same configuration as those shown for those three stages in figure 19-4. An additional 6BA6 RF preamplifier is provided for higher gain and better selectivity. A pair of 6AQ5 tubes provides push-pull output. The second 6AV6 placed ahead of the lower 6AQ5 grid circuit inverts the audio signal for grid drive, with "approximately unity gain," determined by the tapped grid leak (470K/8200 ohms) in the top 6AQ5 circuit. This particular circuit is a classic example of older home entertainment engineering, and there is much to criticize in its selection over the use of a twin-triode balanced paraphase using a 12AX7 or a 6SN7. Why was it chosen? Habit, probably---it was a good choice for 1932. The main feature of this set which differs from AC-DC configuration is, of course, the use of a power transformer and a 5Y3 full-wave rectifier. The configuration of the rectifier circuit was one of the earliest and most durable circuits in the history of tube-type home entertainment radio. This later configuration uses a 5Y3 instead of an 80, has larger filter capacitors (20 mfd rather than 8 or 10 mfd), and a resistor in place of an inductance between the two filter sections. Older radios most often used a speaker field coil between the two filter sections, partly because Alnico magnets were not available until the late thirties, and partly because inductance at this point compensates for using smaller capacitance values to get good filtering. Note the configuration of the screen circuit for the 6BE6 and two 6BA6's. All three screens are connected together. This is poor design, and likely to cause parasitic oscillations. The circuit in figure 19-4 also shows the screens connected together, but in this instance, there are only two screen, in stages that operate in opposite phase, so any coupling between the two stages has a negative feedback effect. Connecting the RF and IF screens together through a long piece of wire can cause significant interaction between the circuits. Perhaps it is your FAQ editor's lot in life, but two of the three radios I have worked on recently have had parasitic oscillation problems, which were difficult to debug and correct. Older radios: Home entertainment radio began in 1920. KDKA in Pittsburgh generally has gotten credit for being the first commercial broadcast station. The two major receiving tubes available at the time with the UX201 and the UV199, as they were called at the time. The UX201, later revised and called 01A was a low mu triode. The V99, as the UV199 came to be termed, was derived from a telephone amplifier triode, developed during WWI. Several manufacturers built sets, but the most predominant in the collector market is the Atwater Kent neutrodyne TRF set using 01A's driving headphones. A standard inexpensive set used regenerative feedback to achieve gain. These were prone to oscillate, squawk, and whistle, and created no end of radio frequency interference, and rapidly lost favor, particularly in high-density metropolitan areas. The first commercially significant superheterodyne receiver was the RCA "catacombs" receiver of 1924. This set used V99's, a 42 KC IF frequency, and a headphone-driving-a-horn "loudspeaker." Both the A-K and the RCA sets required three DC voltage supplies. The A supply (5 volts DC for 01A, 3.3 volts DC for V99) heated the filaments. The B supply, typically 90 volts, provided plate voltage. The C supply, ranging between 9 and 15 volts, and connected as a negative supply, was used to bias the tube grids. RF gain was controlled by a rheostat which controlled the filament voltage. These three voltages were supplied by lead-acid storage batteries, with a Tungar bulb charger for charging the batteries when the radio was not being used. All of the RF stages, and the catacombs superhet local oscillator, were tuned by separate dial knobs. If this sounds like the definition of a kloodge, it was. I had examples of both an O1A Atwater Kent and an RCA "portable" (ran on dry batteries) catacombs set, complete with lead-acid batteries and Tungar charger, at the end of WWII. These sets sold by the thousands, but were obsolete by 1929, and most of them were discarded when their storage batteries wore out. Worth noting that "Philco" is a contraction of "Philadelphia Storage Battery Company." It is also worth noting here that RCA, or "Radio Corporation of America," was not a separate company until 1929, but a patent pool and sales company owned by General Electric, Westinghouse, and AT&T. The phonograph fans will, no doubt, describe how the Victor Talking Machine Company and Radio Corporation of America became RCA Victor. Automatic volume control methods were developed around 1925. AVC, which is synonymous with the term "Automatic Gain Control" (AGC), allowed sets to operate at much higher input sensitivity, and to reduce that sensitivity to prevent overloading in the presence of a strong signal. Methods of tracking RF stages and a local oscillator operating at some difference frequency were also developed in the mid-late 1920's. The final developments needed to build a mains-powered single knob tuning "modern" superheterodyne radio were filaments capable of working on AC without developing hum, a suitable high-voltage rectifier, and a tube with high plate resistance. The first two appeared around 1928 in the form of the 26 and 71A tubes and the 80 rectifier. While these were not the actual "first" devices, they appear in almost all of the early mains-powered radios. The third came about a year later in the form of the UY224 tetrode, later known as the 24A. The 24 also had another recent innovation, the indirectly-heated cathode, which allowed the cathode element of each tube to "float" at a different voltage from the heater supply DC reference. Problems with secondary emission from the 24 were "cured," more or less, by processing the plate material to reduce this emission. This produced the 24A. However, a more permanent fix was to include a third grid to "suppress" the reverse current resulting when plate voltage was lower than screen voltage. The 57 and 58 pentodes were the result. Both have 2.5 volt indirectly-heated cathodes. However, the 58 has a characteristic known as "variable-mu." Actually, with pentodes, one considers transconductance, and what "variable-mu" actually does is to reduce the transconductance as the tube is more heavily biased. The feature is desirable in circuits with AVC. These pentodes showed up around 1931. The pentode power amplifier was also introduced around the same time, with the 47 replacing the 45 in many designed of the 1932-34 era. The last significant development in tube design for AM broadcast radios was the development of a single tube with two control grids to serve as a self-exciting local oscillator and mixer amplifier. The 2A7, quickly replaced by the 6-volt-heater equivalent 6A7, was the predominant design, and the 6A7 was used very commonly until after 1940. The 6L7 also was introduced fairly early. This is a mixer that is not designed to operate as a self-oscillator, and was used, particularly in communications sets, with a separate local oscillator, until the 1950's. Availability of a single tube for the superheterodyne oscillator-mixer function was essentially the death-knell for TRF designs. Another contemporary development which entered production in 1933 was the 2E5 "tuning eye" tube, which varied a shadow area on a visible target as an inverse function of the control grid voltage. TRF sets were built into the 1950's, but are not very common. They tend to be either very cheap radios for use in metropolitan areas with strong signals or in high end sets where the broad bandpass allowed "high fidelity" (though the AM stations actually only transmit a signal that has 5KC as the 3db half-power point in the modulation). Availability of components for a vibrator power supply made automobile sets operating from 6 volts DC practical. There was a wholesale switch >from 2.5 volt heaters to 6.3 volt heaters in 1934. The 2.5 volt heater series of tubes quickly became obsolete. The switch to 6.3 volt 300 ma. filaments was parallelled by development of a two-diode rectifier and an output tube with 25-volt 300 ma. heaters, making series string wiring of the heater circuit practical. These are the 300 ma. heater transformerless sets described above, which date from about 1934. Octal-based tubes enter the picture in 1936. Many of the original designs were built in self-shielding steel envelopes. Metal octal tubes were built with a flat "button" glass seal, which allowed much shorter electrode lead connections. Early glass octal tubes continued to use the older "press" design, with relatively long leads. RF and AF tubes in the original octal series had small top caps for connection to their control grids. It was not until about 1939 that single-ended tubes entered production. Development of a button seal that could be used with glass envelopes allowed manufacture of metal-based "loctal" tubes. These entered production in 1939. At the same time, a cylindrical bulb for glass tubes also entered production, allowing closer spacing between tubes. Experimental FM became a commercial broadcast enterprise in 1940. The original FM band began at 42 megacycles, and production of home entertainment receivers to receive that band began in 1941. The band originally overlapped the experimental television band (later channel 1, 48-54 megacycles). The FM band was reallocated to 88-108 megacycles in the spring of 1945, thus a set with 88-108 capability is postwar. Another "strictly postwar" feature is the 7-pin miniature tube. The 9-pin miniature followed around 1949. A few tubes were "survivors" through the 1928-50 period. The standout among these is the 80 rectifier, which was still being used in new production in the mid-1950's. The 5Y3GT which replaced it is nothing but an octal-based version of the 80. The 2A3 and 45 power triodes, as well as the less-common 6A3 were all used from the early 1930's until well into the 1950's, and there remains today, something of a cult that believes that these triodes are the only audio power tubes worth considering. All of these tubes use filaments cathodes, and the most practical circuits for using them required a separate filament winding, elevated to the 40-60 volts needed to bias these tubes near cutoff. Beam power tetrodes were introduced as octal tubes, although the 807 (very rarely seen in the home entertainment market) continued to use the older large 5-pin base. The principal beam power tetrodes were the 6L6, 6V6, and 25/35/50L6. The 6L6 in a push-pull circuit required more current than a 125 ma. 80 could provide, and presence of a pair of 6L6's with a bigger rectifier means a "high-end" set. Push-pull 6V6's could be supplied by an 80 and provide very adequate audio power of good fidelity to the open-mounted loudspeakers used in virtually all home entertainment equipment until the mid-1950's. Generally, a push-pull power output stage, using any pair of triodes, beam tetrodes, or pentodes, means a quality set with other desireable features, low hum, and good sensitivity. -- *********************************************************** Hank van Cleef vancleef@bga.com vancleef@tmn.com *********************************************************** From vancleef@bga.com Thu Dec 15 02:20:30 EST 1994 From: vancleef@bga.com (Henry van Cleef) Subject: FAQ rec.antiques.radio+phone (part 4 of 5) Date: 14 Dec 1994 01:28:29 -0600 Lines: 211 Message-ID: <3cm6qt$228@ivy.bga.com> Summary: Part 4 - Sources of spares and services for old radios. Rec.antiques.radio+phono Frequently Asked Questions Revision Date Notes 2.0 11-1-94 Revised version from Aaron Field. (this version was previously posted to the newsgroup). ------------------------------------------------------------------------------ Subject: FAQ part 4/5 repost (updated) Lines: 196 Q: Where can I get tubes, electronic parts, knobs, dial lenses, grille cloth, schematics, literature, refinishing supplies, etc.? A: *********************************************************** * THE VINTAGE RADIO SOURCE LIST * * (update: 10/17/94) * * Comments, suggestions to: a.field@uicvm.uic.edu * * Aaron S. Field, M.D., Ph.D ("The Scrounger") * *********************************************************** The following suppliers carry a variety of merchandise for collectors and restorers of vintage radio/phono/TV/jukeboxes. Catalogs or inventory lists are available from all of them. Following this list is a directory of commonly needed items, with additional sources. 1. Antique Electronic Supply, 6221 S. Maple Ave., Tempe, AZ 85283, (602)820-5411: Great source for tubes, components, restoration supplies, books, etc. If you're new to the hobby, start with the AES catalog--it's indispensible! 2. Puett Electronics, P.O. Box 28572, Dallas, TX 75228, (214)321-0927: Incredible supply of literature and service data, also some parts. Good source for collectors of E.H. Scott and McMurdo silver radios. 3. Play Things of Past, 3552 West 105th St., Cleveland, OH 44111, (216)582-3094: Plenty of hard-to-find parts for the earliest radios, including rare tubes. (Probably the best source for original parts on 1920's sets.) Lots of literature as well. Excellent catalog. 4. Old Tyme Radio Company, 2445 Lyttonsville Rd., Silver Spring, MD 20910, (301)585-8776. Tubes, vintage parts, radios, test equipment. 5. Great Northern, P.O. Box 17338, Minneapolis, MN 55417, (61) 727-2489: Lots of stuff for collectors of Zenith radios-- parts, literature, T-shirts, service data. 6. Vintage TV and Radio Supply, 3498 W. 105th St., Cleveland, OH 44111, (216)671-6712: Nice selection of books, tubes, knobs, components, refinishing supplies, etc. Much better knob selection than AES (#1 above). Good catalog. 7. Wade's World of Knobs (Wade and Joe-Ann Terrell), 7109 E. Arbor Ave., Mesa, AZ 85208, (602)830-7849: Reproduction plastic knobs and dial lenses, etc. 8. Antique Radio Labs, R1, Box 41, Cutler, IN 46920, (317)268-2214: Limited selection of various parts and literature. 9. Don Diers, 4276 North 50th St., Milwaukee, WI 53216-1313: Nice selection of tubes and vintage parts. Tons of caps! Fun to read catalog! 10. Triode Electronics, Box 578751, Chicago, IL 60657, (312)871-7459: Jukebox needles, cartridges, tubes, other parts. 11. A.G. Tannenbaum, P.O. Box 110, East Rockaway, NY 11518, (516)887-0057: Vintage parts and literature, test equipment. Additional sources are contained in the following directory of commonly needed items. The list is currently geared mainly towards radio, but phono/TV/jukebox collectors should find useful sources here as well. The sources listed above are referred to by number. Books-- Best source for currently published books on collecting and restoring radio/TV/phono etc. is #1! For vintage literature, see "Literature" listing below. Capacitors-- #1, #6, #10 all have good selections. #10 may be the best. Custom rebuilds on single or multi-unit can caps are available from: Frontier Electronics, 403 S. McIntosh St. or Box 38, Lehr, ND 58460, (701)378-2341. Price list available. Coils-- #1,3,4,6,8,9 all have various coils, chokes, and transformers, both originals and replacements. (Try #3 first for original 1920's and 30's stuff). Decals-- Decal reproductions of the following logos are available from #1,4,6 (and probably others): Philco, Atwater Kent, Zenith, Stewart-Warner, RCA, Stromberg-Carlson, Admiral, Emerson, GE, FADA, Garod, DeWald, Belmont, Sonora, Magnavox Lion (for horn speakers). Dials-- Reproduction tuning dials available from: Antique Radio Restorations, 635 S. Lincoln Ave., O'Fallon, IL 62269, (618)632-7423. (AK, RCA, Zenith, Philco) Also try #1,2. Dial covers-- Reproduction dial covers custom made from broken cover or tracing: a. #7 b. Doyle Roberts, HC-63 Box 236-1, Clinton, Arkansas 72031, (501)745-6690. c. Old Time Replications, 5744 Tobias Ave., Van Nuys CA, 91411, (818)786-2500. Limited selections of original dial covers available from #1,2,4,6. Dial pointers-- #6 has a few generic replacements if you can't find an original. Grille cloth-- a. Good selections from #1 and #6. Sample cards available. b. John Okolowicz, 624 Cedar Hill Rd., Ambler, PA 19002, (215)542-1597: "Deluxe Replica Grille Cloth" (Philco, Emerson, Scott, Zenith). Knobs-- Best selection of reproduction knobs from #6 (check here first for clock radio knobs) and #7. #1 not bad for Zenith and Philco. Most suppliers say "many available, send us your request". Lamps-- #1,3,6 and 9 all have good selections. Literature-- #2 and #3 have impressive archives of vintage radio literature, with titles listed in their catalogs. #1 and #6 have reprints of popular service manuals and repair data (AK, Philco, Radiola, Zenith). Also see "Schematics and Repair Data". Periodicals-- a. "Antique Radio Classified" (monthly), PO Box 2-V32, Carlisle, MA 01741, (508)371-0512: Classified ads, radio supplier ads, articles, meet announcements. b. "The Old Timer's Bulletin" (quarterly, with membership in Antique Wireless Association), dues $12.00. Contact AWA, Box E, Breesport, NY 14816. High quality publication chock full of articles on all areas of vintage radio, including broadcast, communications, telegraph, TV, etc. c. "The Radio Collector" (monthly), PO Box 1306, Evanston, IL 60204-1306, (708)869-5016: published by Marc Ellis, antique radio columnist for "Popular Electronics" for many years. Regular features include repair and restoration advice, vintage book reviews, company chronicles, Q&A, classifieds. $20.00/yr. Highly recommended. d. "Radio Age" (monthly, with membership in Mid-Atlantic Antique Radio Club), dues $20.00. Contact MAARC, Roy Morgan, PO Box 1362, Washington Grove, MD 20880. "Radio Age" was its own publication until its recent merger with the "MAARC Newsletter". e. There are many radio clubs across the US, each with its own newsletter! Refinishing supplies-- #1 and #6 supply all manner of chemicals (fillers, polishers, lacquers, etc.) for refinishing both wood and plastic cabinets. Repair and restoration services-- There is probably a collector's club near you that can steer you towards an individual in your area who works on vintage equipment. Otherwise, if shipping your radio is an option for you, try the following: a. For Your Listening Pleasure, 368 Clinton St., Binghamton, NY 13905, (607)797-0066. Four levels of restoration are available, from "working order only" to "museum quality"! b. #3 and #4 do repairs--not sure about cabinet restorations. c. Sunrise Services, 2343 Ballycastle, Dallas, TX 75228, (214)328-4249. Radio cabinet refinishing, wood or plastic. d. Check "Antique Radio Classified" for countless ads for this type of service! Schematics/repair data-- Most schematics on vintage radios come from either the Rider's Perpetual Troubleshooter's Manuals (earlier sets) or the Howard Sam's Photofacts (post-war sets). These are available in many public libraries. Otherwise, the following suppliers offer schematics at reasonable rates (if you can provide them with a model number): #1,2,4,5. If you don't have a model number but can provide the tube #'s and layout, for an extra fee they can usually find the right schematic. See also "Literature". Tubes-- A complete list of tube suppliers would be an incredible headache to compile. Just about all of the suppliers listed at the beginning of this directory have tubes, and it is unlikely that you would be unable to get what you need from at least one of them. The ones that have their inventory conveniently listed in their catalog are: #1,2,3,6,9. Prices vary. *********************************************************************** Watch rec.antiques.radio+phono for future updates to THE VINTAGE RADIO SOURCE LIST! Comments and suggestions welcome: a.field@uicvm.uic.edu Aaron S. Field, M.D., Ph.D. ("The Scrounger") *********************************************************************** -- *********************************************************** Hank van Cleef vancleef@bga.com vancleef@tmn.com *********************************************************** From vancleef@bga.com Fri Dec 16 10:21:20 EST 1994 From: vancleef@bga.com (Henry van Cleef) Subject: FAQ rec.antiques.radio+phone (part 5 of 5) Date: 16 Dec 1994 02:13:19 -0600 Lines: 878 Message-ID: <3cri6v$g0b@lia.bga.com> Summary: Part 5. - Frequently-asked technical questions about vacuum tube electronics. Rec.antiques.radio+phono Frequently Asked Questions Revision Date Notes 1.1 Oct. 24, 94 Revised and reordered as part 5. 1.1 Dec. 12, 94 Minor edits, added new material on caps and tv Part 5 - Radio and electronic phono technical questions. ------------------------------------------------------------------------------ FAQ editor: Hank van Cleef. Email vancleef@bga.com, vancleef@tmn.com This is a regular posting of frequently-asked questions (FAQ) about antique radios and phonographs. It is intended to summarize some common questions on old home entertainment audio equipment and provide answers to these questions. Q. I've got a very nice Philco tombstone radio that is only a decoration because it doesn't play. What can I do to get it to play. A. This section of the FAQ addresses getting them to play as nicely as they look. While not intended to be a comprehensive primer, this section covers many questions that come up regularly. The topics discussed in this section of the FAQ presume that you have a working knowledge of vacuum tube circuits. Q. Why does a 35Z5 or 35W4 rectifier have a number 40 or 47 bulb connected across part of the heater? A. The heater serves as a voltage divider. Resistance of cold filaments is much lower than when they are hot, and connecting a bulb in series will put almost the whole 110 VAC across it until the heaters warm up. The plate current flows through the bulb/heater to balance the current once the tubes are warmed up. Note that this also applies to ballast tube setups---the ballast resistance is designed to increase as the set warms up. It's a way of putting a cheap light bulb in a cheap radio. (Historical note: This is an interview question I used to use when interviewing engineering applicants in the fifties and sixties). Q. I just found a (very old tube) radio in a (barn, attic, junk sale, etc.). It's complete. Can I plug it in and see if it works? A. If you didn't hear the radio playing, it would be very wise to do some resistance checking first. a. What is the condition of the line cord? Replace it if it is frayed or the rubber is petrified. b. Condition of filter capacitors. Wet electrolytics, which were used in the 1930's, should be replaced without question before applying any power. These are identifiable by the metal cans with vent holes on them. Dry electrolytics (which aren't really dry inside) can also lose their film and be low resistance. If DC resistance between the B+ line and circuit ground (this may not be chassis ground) is not 500K or more, find out why. Make sure the speaker is included in this check if it has a field coil or has the output transformer mounted on it. With electrolytics and any voltage divider resistors out of the B+ circuit, DC resistance should be several meghohms. c. If it's an AC-DC set, check to see if one side of the line is wired to the chassis. Many of them were. If so, keep the set away from any metal objects to avoid shock hazard. Some of the early AC-DC sets would hum like crazy if they were plugged in with the chassis "hot." d. If it's an AC set, consider installing a fuse in the line circuit. 2 amps 250 volts for sets with 80/5Y3, 4 amps 250 volts for sets with 5Z3/5U4. e. Do a cosmetic inspection. You'll want to vacuum off any old dust, dirt, cobwebs, etc. first. Look for things like charred resistors, melted wax from capacitors, coils, and transformers, and any indications that the radio go put in the (barn, attic, etc.) because something was wrong with it. f. Take a look at the bias circuit for the power output stage. See below for discussion of typical bias circuits. If there is an electrolytic in the circuit, make sure it isn't "low ohms." If your output stage is 6L6's, or if it is filament tubes like 2A3, 6A3, 45, or 47, take a very good look at things. A few hours spent doing a good visual inspection and some ohmmeter checks can pay off handsomely. If you've got to replace a charred resistor, find out what burned it out and fix that too, before applying power to the set. Remember that 99% of vacuum tube failures are due to open heaters or filaments. The other 1% are due to gas or interelectrode shorts. This leaves the item that tube testers have a big BAD-?-GOOD meter to measure, emission, down in the mud as a tube fault that makes a radio play poorly. Except for rectifier tubes that have been "sucked dry" by a gassy output tube or shorted filter cap, most of the tubes I have diagnosed as causing problems because of low emission would not exhibit that low emission in a tube tester. Example: a 6SQ7 diode that quit conducting after 15-20 minutes of playing. Diagnosis was confirmed by soldering a 1N34 diode across the terminals. If the getter material (you can see it on glass tubes) is white instead of silver, the tube is probably gassy----most common on power output and rectifier tubes. A few sets used gas-filled rectifiers. The 0Z4 is most common in auto radios, but you may find and old set with an 82 or 83 mercury vapor rectifier. Also remember that with tube equipment, DANGER, HIGH VOLTAGE. applies. In home entertainment transformer sets, we are talking about as much as 500 volts, and most smaller transformer sets used somewhere between 250 and 350 volts as the main B+ voltage. The transformerless sets generally provide 135 volts, and have the mains power (to use the British term) hooked directly to various circuits and perhaps the chassis as well. Q. The chassis of my radio is covered with a thick layer of dust, fine dirt, and underneath is a film of brown crud. How can I clean this thing up without damaging it? A. This particular topic gets a lot of discussion and advice, some of it very bad. Your radio has some irreplaceable components, and if you use the wrong methods, you can make a junker out of a restorable set in a hurry. There are some things to keep in mind: a. The chassis is probably cadmium-plated steel. A few radios were made with nickel-plated steel (looks green when corroded), copper-plated steel, or chromium-plated steel. A few chassis were made of aluminum. If it is a dull silver color, check with a magnet. An aluminum chassis is non-magnetic, all of the steel chassis are magnetic. b. The dial face may be a water-soluble paint or a decal. c. Colored knob markings (lines and dots, as well as letters filled with color) may be water-soluble. d. Any silk-screened surface markings may come right off. These include tube layout information on the chassis, inspector's marks, and other printing. e. The tuning mechanism may be stiff because of petrified lubricant in various shafts and rotating elements. f. Coils, IF transformers, and tuning condensers may be difficult or impossible to replace if you damage one. g. If the radio is complete, tubes in place, the crud and dirt is on top of everything, not in the electronics. You want to get it off the radio, not melt it down so that it flows into the working parts. You can remove the tubes. Make sure that the tubes are clearly marked as to tube type, and make sure you have an accurate diagram so that you can replace the tubes in the same sockets you removed them from. Get a pencil and piece of paper and make notes about things you move, disconnect, or take apart, so that you can get everything back together the way it was originally. Begin by vacuum cleaning the set, and use a soft brush to loosen dirt while keeping the vacuum nozzle near the brush so that it will pick up loosened dirt. If you find mouse droppings, be prepared to examine the set closely for damage from mouse pee. Gently brush off the tuning condenser, being careful not to bend the plates. Once the surface dirt is off, you can begin to consider how best to remove the crud, and how far to go with the cleanup. There are two things that are very poor to use around electronics: steel wool and soap-type detergents. Steel wool will shed little particles and raise havoc. Soaps and liquid detergents leave residues that can be hard to remove. Liquid detergents also do a fabulous job of softening and removing silk screen inks, water soluble dial markings, and tube markings, even those that may be safely soaked in water for a few minutes. Start on the chassis crud by using a damp rag moistened with plain water. Don't slosh water onto things. Most tap water is safe to use around electronics, and is an excellent solvent. I note that I have refurbished electronics that have been immersed for days in fresh water after they have been allowed to dry out, and found very little damage, mostly to capacitors. If the crud comes off with water alone, continue with the damp cloth treatment. It may be slow, but it will leave a clean surface with little residue. Finish the job with moistened Q-tips to get into various nooks and crannies. Be careful that you don't remove marking inks and paints. A stronger alkiline solvent is clear household ammonia. This also evaporates without leaving a residue. If water is not melting the crud, try a little ammonia on a Q-tip. Use the ammonia straight, and if it gets results, use it on a damp rag to moisten the chassis. Generally, once ammonia-sensitive crud has been melted, it will come right off using a rag dampened with water. Be careful not to get ammonia on a shellac wood finish---it will cut the shellac and leave marks. If this doesn't get results, try a mild acid---clear cider vinegar. Use the same methods as with ammonia, finishing with a rag dampened with water. By this time, you should have most of the removable crud off the chassis. Some other solvents to try---only in small areas with Q-tips: Isopropyl alcohol. This dissolves a great many things, including flux rosin, some marking inks, etc. Trichloroethane (GC Electronics "Chloro-Kleen"). Also dissolves many things. Don't use on plastics until you have checked to make sure it is safe. Chloro-Kleen works very well on phenolic and ceramic-mounted switches such as bandswitches and pushbutton switches. Lacquer thinner. This is a "court of the last resort." It is a powerful solvent that will damage many plastics, remove a lot of marking inks in a jiffy, and generally raise merry hell if you get it in the wrong place. Use on metal parts only. Also pay attention to the various warnings about flammability and use only in well-ventilated areas. Corrosion on cadmium-plated chassis generally does not respond very well to anything. You can use Naval Jelly to improve the situation, particularly if there is visible rust. Light fingerprints often will respond to automobile polish (Dupont No. 7 is good). This treatment (followed by an application of Simoniz paste wax) will make many lightly-scratched plastics look like new. The best solvent for use with petrified lubricants in tuning mechanisms is diesel fuel. If there are separately-mounted shafts or gear mechanisms, you can often take them off----just make sure you can get them back on again, and positioned properly. Watch for spring-loaded double gears in gear mechanisms that need to be preloaded when you assemble them. Shafts should be relubricated with a light grease like white Lubriplate---use only enough to leave a film on the parts needing lubrication, and wipe off the rest. Gear trains generally work well with a little 3-in-1 oil on axle pivots and a film of lubriplate on the gear teeth. A stiff volume or tone control will generally respond to a drop of 3-in-1 at the end of the bushing---use only a drop, and wipe it off after about 5 minutes. Tube washing gets a lot of attention. Keep in mind that washing most tubes won't make them work any better. Before you start, make sure that the tubes are clearly marked as to what they are. While there is no mistaking a 6A7, a T-9 beam power pentode with no markings may be a a 6W6, a 25L6, a 35L6, a 60L6, or a 6V6. A 50L6 plugged into a 25L6 or 35L6 socket can produce interesting symptoms that can be very hard to diagnose. Contrary to popular opinion, tube markings on glass will come off, some more easily than others. During the 1950's and 60's, tubes were specifically marked with easily removable markings in an attempt to thwart a grey market in used tubes being washed, reboxed, and sold as new. Generally, just holding the tube under flowing water will rinse off most of the dirt--- a little help from rubbing the surface with a thumb where it is not marked generally gets fine results. Use a china marker to marked the type on any tube that isn't clearly identified, and let them dry thoroughly before reinstalling. Tubes that are loose in their base, or have a loose top cap, respond to squirting a little superglue into the gap. Make sure, in the case of a loose base, that the leads aren't twisted (and shorted). Q. What about AF power amplifier bias circuits? A. You can do a little inspecting to see what your radio uses. a. By far, the most common circuit is to use a cathode resistor with an electrolytic capacitor for AC bypass. This is what you will find in all of the transformerless sets. AC bypass is less critical in push-pull output stages, although most of them operate class AB (i.e, both tubes biassed near cutoff). If the capacitor is shorted, the output tubes will over-dissipate and their plates will glow red in a few minutes. If the capacitor is open, audio output will be low and distorted. b. Back bias. I was somewhat surprised in checking Terman "Radio and Electronics Engineering" 4th edition (1955) not to find this circuit. It uses a power resistor in the B- return to develop a bias voltage, typically 10-30 volts, and may be used in conjunction with the cathode resistor self-bias circuit. The center tap of the power transformer will be connected to one end of the power resistor and B- circuits will be connected to the other end. On sets using filament power tubes, the filament supply may be connected here, and the power tube grids returned to the power transformer center tap. Most of the bias voltage is developed by output tube plate current. If there is a leaky electrolytic here, it will generally overstress this resistor and burn it out. c. Separate "C" bias supply. In this case, the set will have second rectifier tube, filter, etc. These are not common in home entertainment equipment, much more likely to be found in theater and public address amplifiers. Q. OK, I've checked that the tube heaters are continuous, that the filters are OK, and generally walked through and done the visual and ohmmeter inspection. I want to plug it in. What do I look for? A. This is the moment of truth, even for an old grey-hairs. Fortunately, tubes will take abuse that transistors won't tolerate. But you want to have your eyes and ears wide open, and be prepared to shut the thing back off instantly. Some people like bringing them up on a Variac, which is an expensive piece of equipment unless you are in the restoration business. So I'll assume you are going to plug the thing into the 100 volt line, turn it on, and see what happens. Make sure you have some sort of antenna connected on sets without a built-in loop. a. On AC-DC sets, turn it on. The tubes should light up, and in 10-15 seconds (when the rectifier and power tube heaters warm up) you should hear 60 cycle hum in the loudspeaker. Indeed, hum is a built-in feature of these sets. If it is overwhelming, you've got a bad filter cap. Check for smoke signals and signs of overheating. If you can tune in a station, you are probably in business. On 35Z5/35W4-type radios, if the pilot lamp burns out after the set warms up, you've got a short in B+ somewhere---probably a shorted filter cap. Turn the set off and find the problem---if you've got a short, the rectifier heater will take the load and burn out after a while. b. On transformer sets, I like to connected a 600 volt DC meter across B+, preferably in the supply to the IF screen grid or plate. If the rectifier is a filament type (80, 5Y3, 5U4, etc.) you'll see full B+ a couple or three seconds after turning the set on, and it should drop to about 100 volts on the IF screen when the cathode tubes warm up (around 10 seconds). Check for smoke signals, burning, and that all the heaters glow. A low level of 120 cycle hum is to be expected, though a really fancy set will give almost no hum at all. Once again, if you can tune in a station, you are probably in business. Watch in particular for a violent purple glow in tubes, particularly the power output and rectifier, plates beginning to glow red, and other signs that there is a short circuit. If the radio doesn't play, keep a close watch on things, although if you have good B+, no gassy tubes, and no red plates, and things are OK after five or ten minutes, you are probably safe in continuing on to do trouble-shooting. A few sets use tubes with mercury vapor in them, which normally glow purple between the elements. Typical are the 83 (not 83-V) and 0Z4 rectifiers, and the gas-discharge VR tubes (0A2,0C3, etc.). Trouble-shooting. If all the tubes light up, you've got B+, and no smoke signals, you can begin your walk through the radio. If the radio is completely dead---no stations, no static---try rocking the bandswitch if the radio has one. Also, the volume control, any tone controls, etc. I've found that on ancient sets, it's a good idea to walk right through and do voltage checks everywhere, no matter how well the radio seems to play. If you have a schematic with voltages marked on it, so much the better, although some of the voltages given by manufacturers can disagree rather markedly from actuals that can be figured by reverse-engineering the design. a. Power output stage: Check screen and plate voltages. These should be close to B+ at the rectifier. Check for positive bias voltage at the cathode on self-bias circuits or negative voltage at the grids if separate bias. b. Audio amplifier. Usually a triode. If the 6SQ7 diode-amplifier type, the only thing to check is plate voltage, which should show a drop across the plate resistor. On resistance-coupled output circuits, make sure the coupling cap is not leaking current to the output tube grid circuit, which will pull up the grid voltage and make the output tube plates glow red. Probing the AF amplifier grid won't show any voltage, but should make plenty of noise in the speaker. c. IF amplifier. Check for screen voltage. If you don't have any, you've got a shorted bypass cap and a dead radio. Plate voltage should be near the supply voltage (generally fed by a blue wire to the 2nd IF transformer). Cathode should show some bias being developed (i.e., plate current through the tube). The grid will generally show the AVC voltage, though your meter will shunt a lot of it. d. Mixer. If the pentagrid type, tetrode, or pentode, check screen voltage. Q. My old radio has a lot of tubes covered with wax, and some of the wax has melted out and is on the bottom of the cabinet. What should I do about this. A. These are inexpensive wax-impregnated paper-dielectric capacitors. They were notorious, even when fairly new, for developing opens, shorts, intermittents, high dissipation, and tend to be rather fragile as well, particularly when soldering around them. Melted-out wax is common, and may be only the result of heat developed under a chassis in normal operation. From reliability and other engineering points of view, replacing all of them with newer capacitors of other types is part of a refurbishment/overhaul. Some collectors feel that 40-60 year old capacitors are "survivors," that wholesale replacement is unwarranted. Also, there are two schools of thought on replacing components with others that are very dissimilar-looking, even in areas that are not normally visible when a radio is installed in its cabinet. A few restorers go so far as to melt the wax out of old capacitors, remove the foil-paper "innards," install a new capacitor, and refill the body with wax. Other restorers feel just as strongly that consistent appearance is more important, and that 100% replacement with no attempt to disguise the appearance of new components is to be preferred. Whether to do a wholesale replacement or not is a decision you'll have to make yourself, and whether to use modern radial-lead components or to try to find lookalike replacements or disguise the new ones, also has no uniform consensus. Your radio may not give you much choice about wholesale replacement. If you find more than one or two bad ones, or if the set has mysterious ills, parasitics, or poor performance, or is intermittent, 100% replacement is indicated. If the item you are repairing is "blue collar" or "high tech," 100% replacement with obviously new good-quality components seems to be preferable. By "blue collar," I refer to test equipment and items such as Hammond organs and studio equipment that worked for a living. By "high tech," I mean good communications receivers and genuine high-fidelity equipment. Many of these items used higher quality components originally. One item that has complete consensus is quality of workmanship. You will want to learn how to remove component leads completely, clean up old terminals, and make neat new solder joints. Q. I found an RCA model 630 ten inch TV set at a flea market. The power cord is shot, and when I pulled the chassis out, I found the wires to the switch appeared to have had the insulation burned off. I found that the 5U4 plates were melted together. I put in a new 5U4 and plugged the set in, but it doesn't do anything---no picture, no sound. What should I do now? A. First of all, a TV set draws substantially more power than a radio. Do yourself a favor and install a fuse in the primary power wiring to the switch. Use a slow-blow fuse rated at about 150-200% of the set's power consumption. For a set drawing 250 watts, a 4 amp should give reasonable protection. On a 630, there is a black box mounted on the left rear of the set, with some power resistors inside. Open the box and check the resistors. These are back-bias resistors, in the B- circuit. If they are open, check all the filter caps. Replace the resistors, if necessary. Bringing up an old TV takes some care, and the order in which you check things out is important. As with all old electronics, assume that it has several things wrong with it. Check that the CRT heater is continuous (ohmmeter)---you should be able to see it glow when you turn the set on. The first thing to fix is the power supply. Once you have good B+, and all the tubes are lit up, do you have a raster? If not, check the horizontal oscillator and amplifier. Note that the horizontal amplifier has very high voltages in it, and that some faults may cause these high voltages to appear where they shouldn't be. Don't go probing around in the horizontal circuit with the set turned on. Horizontal amplifiers on magnetic deflection sets ran with voltage and current levels appropriate for a transmitter, and several postwar sets continued to use the 807 beam tetrode as a horizontal amplifier tube, rather than one of the purpose-built tubes. Shut the set off, connect your probes, then turn the set on, take your readings, then shut the set back off again. Don't touch anything in the set without first assuring that it is shut off, then touch an insulated probe connected through a 1K resistor to ground to all of the terminals in the circuit to assure that there isn't a high voltage charge somewhere. If the horizontal circuits are OK, the 1B3 high voltage rectifier filament will glow. Make sure that the high voltage cable isn't shorted somewhere, and that there isn't a lot of dust or crud to bleed off the high voltage---problems here are usually pretty obvious in the dark, where you can see corona discharges, arcing, and other leakage problems. Unless you have equipment of measuring 10KV, you can't measure the high voltage directly, but if the 1B3 filament is lighting, and the flyback plate winding to the 1B3 is not open, you probably have high voltage. If you have high voltage, and the tube does not show any light (this may be a spot or a line, rather than a raster), check the CRT grid-cathode bias voltage---once again, keeping hands completely away from the CRT socket unless the set is turned off and you've grounded terminals through 1K. The brightness control should be able to swing the voltage back and forth from about -20 to -60 volts. Check grid 2 voltage---should be around 250. If you have a horizontal line on the CRT, you are not getting vertical deflection. Check that the oscillator is oscillating, that the output stage is operating. Once you have a raster, then you can start debugging any problems in the video and audio circuits. Prewar and early postwar TV sets trapped the audio right behind the tuner and used separate IF strips for video and audio. Later sets use "intercarrier" IF's, with one IF strip and a sound trap at the end of the IF chain. In either case, "raster, no picture, no sound" means that the problem is between the tuner and the sound trap. "Picture, no sound," or "sound, no picture" means the problem is after the sound trap. Don't fuss with the tweaks on the IF strip (strips) unless you have the proper equipment and instructions for doing an alignment. Unlike most radios, these are stagger-tuned, and you don't just "tweak them up" for best performance. The video comes from a conventional AM detector and a "high fidelity" voltage amplifier, connected to the CRT cathode. Note that the bandpass of the video amplifier is very wide, and the term "video amplifier" has become a generic term from a wideband untuned amplifier. The audio is through a conventional ratio detector and single-ended audio amplifier to a (incredibly cheap setup for something that cost $400 in '46) small speaker. One fairly standard complaint is loss of raster sync. If the tubes are OK, this is generally the paper capacitor bugaboo at work. Loss of both horizontal and vertical means that the coupling out of the video amp has a problem. Horizontal sync comes from differentiating the video signal, and vertical sync from integrating the double-speed interlace "trick" pulses that ride on the "pedestal" portion of the video signal (the vertical sync portion). These are some basic things about forties TV sets. Note that the CRT's on early magnetic deflection sets had offset guns and "ion trap" magnets. This was to prevent burning a spot in the center of the CRT. Around 1948, the aluminized phosphor coating, which was impervious to ion burns, went into production, eliminating the need for offset guns. If the ion trap is misadjusted, the electron beam won't be aimed at the phosphor screen properly, so the raster will be dim or nonexistent, or have "neck shadows" at the edges. This, like the IF tweaks, another "if it's working, don't fix it." Electrostatic deflection sets that used tubes like the 7JP4, did not have ion burn problems, so are mounted with nothing on their necks. These sets also did not require transmitter-like power for horizontal deflection, so did not have high voltage derived from the horizontal circuit. Instead, a separate RF oscillator was used. CRT circuits in electrostatic deflection sets are quite similar to oscilloscope CRT circuits. There are several books on servicing television sets that generally apply to forties sets, although they are generally oriented toward later sets. Compared to later sets, most forties TV sets were powered through transformer supplies, did not have any tricks like B+ boost. Q. My radio plays, but the audio is distorted. Announcers sound like mush-mouths, and music sounds as though gravel is rattling in the instruments. I checked it with another speaker, and it sounds just as bad. A. The most common causes of distortion are in the power amplifier circuit. (Note that in the following I am assuming class A or AB1 operation, where tubes do not draw grid current. If the grids of your power amplifier tubes are driven by power tubes, such as a 6N7 or 6V6's, most of the following applies to operation at low output). 1. Check that the coupling cap (or caps, in the case of push-pull) are not leaking DC from the preceding stage and pulling the output tube grid high. Most circuits use a 180K to 500K grid leak to ground and a .05 or .1 microfarad coupling cap. At low-moderate audio output, there should be no measureable DC voltage across the grid leak resistor. Check the grid leaks themselves for proper value and good connections (typically to ground). Wax paper coupling caps here are notorious for giving problems, and are candidates for replacement even if they appear to be good. The tube itself may be developing excess gas current in the grid circuit. Disconnect the coupling cap, turn the set on, and make sure there is no voltage developed across the grid leak. If there is, replace the tube. Note that most tube testers won't disclose this problem. With larger tubes (6V6, 6L6), replacement tubes made after the mid-70's often had poor gas current characteristics, and some designs were built with higher-value grid leak resistors than specified by the manufacturers on the assumption that replacements would "never be that bad." Most beam tubes specify a maximum impedance in the grid circuit of 500K for cathode bias, 100K for fixed bias operation. 2. Check the value of the cathode resistor. Be careful here, because a resistor that has overheated may not only have changed value, but have charred the color bands so that they look like a very different value resistor. If the circuit uses a cathode bypass capacitor (usually an electrolytic, 20 mfd. 25 volt typical), check that it isn't leaking current, and check that it has capacitance. 4. Check grid bias with the set running. Proper bias for various tubes can be estimated from tabular data in tube manuals, and ranges from around -7.5 volts for a small high-gain beam pentode like a 50L6 to around -60 volts for a large low-gain triode like a 2A3. 5. On a push-pull output stage, check that both sides are operating. An easy check is to jumper across the grid leak resistor with a clip lead, and see if things change. If jumpering one input kills the audio, the other side is inoperative. Prime things to suspect if one side is dead are the power tube on that side, open transformer plate winding (no B+ on that tube), open coupling cap, or problems in the voltage amplifier ahead of the output stage. 6. If you haven't found the problem yet, check the quality of the audio coming out of the preamplifier stages. 7. DC imbalance can cause problems in push-pull circuits. Most old radios don't have any place to measure this. You can wire 100 ohm resistors into the plate circuits, in series with the output transformer, and measure the quiescent DC voltage across them. For most old radios, a 20% imbalance is tolerable. Keep in mind that the voltage developed across a cathode resistor is total cathode current, both screen and plate, and that a common cathode resistor in a push-pull circuit is looking at the effects of two tubes simultaneously. Q. I've got an "All American Five" 50L6 radio that has new filter caps, but the hum that comes out of the speaker is really out of sight. I can hear it in the next room when the volume is so low I can't really hear the station it's tuned to. I know these sets hum, but should it be that bad? All the tubes test good on a mutual conductance tube tester. A. No---you've probably got a very common tube fault that a tube tester doesn't detect, heater-cathode leakage, probably in the 50L6. In these sets, the low end of the 50L6 heater is about 38 VAC above ground, and the high end, up at 88 volts. What you are getting is AC on the cathode, and the only real solution is a 50L6 that doesn't have heater-cathode leakage. 12SQ7's can also have this problem, although they are always wired at the ground end of the heater string. The only real diagnostic is to scope the cathodes of both tubes. One item that aggravates this situation is that many "All American Five" sets had no bypass capacitor across the power amplifier cathode bias resistor. Hanging a 50 mfd. 50 volt cap here often will improve set performance and reduce hum, although it won't solve a serious case of leakage. Before trying to diagnose hum problems, particularly in a series string set, try turning the plug to the wall socket around the other way, to reverse the polarity of the chassis. Many of the older 300 ma. series string sets were very sensitive to primary power polarity, and would have very loud hum if the power plug were connected the wrong way. Q. What sort of tools and test equipment do I need. A. A 20,000 ohms/volt multimeter is indispensible. They are relatively inexpensive, and modern multimeters have protection circuits in them. You can trouble-shoot and fix almost anything discussed in this newsgroup with a multimeter and some knowledge of circuit theory. Many prefer an analog meter with a needle over digital. You can watch the needle move and see what's happening. While not "test equipment," tools for unsoldering and soldering components and wire are also mandatory. Soldering is discussed in another FAQ question. Other small hand tools include screwdrivers, allen wrenches (for knobs with setscrews), nut drivers, and small diagonal cutters and needle-nosed pliers. There is only one kind of tool, a good quality tool. Buy the best. They'll last forever, and do their jobs well. Don't buy cheap knucklebusters. They are hard to use, will make scratches, bend, and break, and scar up the work. Buy the best---many of the good tool manufactures have sold the same tools for over fifty years, and many of us use tools that old today. Beyond the basics are the following: a. Oscilloscope. This has become the primary instrument for use in electronics work of all sorts. While they were not commonly used for radio repair in the 1930's and '40's. There are a great variety of scopes, ranging from the old relaxation oscillator sweep type used in the thirties (and sold by Heath as late as the 70's) to the very latest solid state scopes with triggered delaying sweep and multiple trace vertical inputs. Almost any scope that works is fine for working on old radios and vacuum tube amplifiers. While you can get old vacuum tube scopes for very low prices, keep in mind that you may find yourself trouble-shooting and fixing it. b. RF signal generator. Once again, these come in many sizes and shapes. These are used for aligning tuned circuits (RF and IF amplifiers). For an AM-shortwave radio, you need 100 kc. to around 15-20 mc, with AM modulation capability, and for FM, you should have 88-108 capability as well. A sweep signal generator (i.e., able to swing the frequency back-and-forth over a small range electronically, with a voltage output to drive an oscilloscope horizontal amplifier) and a suitable scope are very nice to have but not mandatory. c. Tube tester. The value of tube testers as a primary diagnostic tool tends to be overrated, but a good mutual conductance tester (Hickock made several) can be of value if it is used appropriately. Cheap "tube checkers" will test filaments (an ohmmeter will do as well) and whether the tube conducts or not, and may detect hard short circuits (these do happen). A Tektronix 570 curve tracer (a specialty oscilloscope that gives graphic displays of tube characteristics) is the ultimate in test devices. However, the ultimate "tube tester" is the equipment in which the tube is used. The function of tube testers, more than anything else, was to sell replacement vacuum tubes. And many really nasty tube-related problems will only show up in the socket in the equipment where they are supposed to function properly. If you have a good scope, multimeter, and signal generator, and know how to use them, you have all the tools you need for radio work. Here are some other items, some of which were popular as radio shop tools, and some of which aren't primarily test equipment. d. Signal analyzer, signal tracer. These were very popular in radio shops. They are an AF amplifier, small speaker, and a diode detector that can be switched in and out of the probe circuit---in essence, a small radio without any tuned circuits. If signal is getting into the antenna, you can probe each stage and hear it, and quickly locate a "dead" or "distorted" stage. e. Condenser tester. Also "radio shop" stuff from the 1930-50 era. An inexpensive L-R-C bridge with an electronic oscillator. Used properly, it can be a handy tool. f. VTVM (stands for "Vacuum Tube Voltmeter"). The virtue of these is the high input impedance (generally megohms) and their ability to measure resistances into the megohms range. Largely supplanted by oscilloscopes, which draw a picture of the signal, but of value today for their ability to measure high resistance. g. Grid dip meter. This is a small oscillator that comes with a set of plug-in oscillator coils that can be poked into tuned circuits. They rely on the fact that a resonant circuit near the oscillator coil will cause the grid current of the oscillator tube to drop, hence "grid-dip." A very simple and handy little device, though generally used with things like transmitters that have to be tuned before power is applied. Since they oscillate, they are also a fine "poor man's signal generator." There were several specialty houses in the US in the 1930-50 era that built very good measurement equipment. I'll mention them by name: Boonton Radio, built Q-meters and R-X bridges. These measure the inductance and other characteristics of RF coils and tuned circuits. Generally used to support coil design efforts. The British Marconi Q-meters are excellent as well. Measurements Corp. Built very nice signal generators, much higher quality than those from repair equipment manufacturers like Hickock. General Radio (Cambridge, Mass.). This company moved to the suburbs in the late 1950's and is now known as Genrad. Their 650 impedance bridge was the general use DC/400 cps L-R-C bridge. It used a small battery and a 400 cps "hummer" (a small vibrator) to generate AC for measuring impedance of things like audio transformers. Over the years, General Radio built a broad line of devices, primarily for engineering use, only some of which are applicable to radio electronics. Guildline of Canada. I mention them because they built some of the very best calibration standards. Their potentiometers and other products are not only "not test equipment" but can easily be damaged if used for testing things. The proper use of such equipment is calibration of working equipment, and the appropriate place for it is a calibration shop. While I mention equipment common in the US, I am familiar with products of Marconi in England, who built engineering support products similar to the Boonton, Measurements, and General Radio products. I believe that Telefunken, Phillips, and Thompson-CSF (spelling?---French company) also built and sold similar equipment. The US stuff often shows up at things like ham swapfests, and is bought and sold by several companies, notably Tucker, of Dallas, Texas. Q. My radio is supposed to have 295 volts on the screen of the 6L6 amplifiers. I read 303.5 on my digital voltmeter. Is something wrong? A. Yes, both your expectation that the screens are supposed to read 295 volts, not 295 +/- 20%, and that your DVM is precise just because it gives you a lot of digits. When was that DVM last calibrated (or was it ever calibrated) against a known standard of some sort? Most shop test equipment is wildly inaccurate to begin with, and has had enough use and abuse (and time) since last checked that you can't trust the readings at all. At best, they will tell you "around 300 volts" or "around 455 Khz" unless you have some way to check against standards. Don't trust anything to be telling you other than "approximately" unless you have had it checked against standards recently, know what accuracies you can expect, and things that can affect accuracy. Most major cities have services which have standards against which to check test equipment, and if you have something like a GR 650 bridge that is working properly, it may be worth the tariff to have it's calibration checked by one of these shops. When selecting test equipment, keep in mind that that nice old Tek scope may have 35 or 30 tubes and 50 adjustments, and pose much more of a maintenance problem than any radio. Q. I don't trust the calibration of my instruments? What can I use to check them? A. There is a good frequency standard available for free: WWV, which broadcasts on 5, 10, and 15 Mhz. If you have a signal generator with a crystal calibration oscillator, you can tune in WWV on a shortwave receiver, tweak the crystal tank circuit, and have a fairly good reference to WWV for other frequencies----though it's a long stretch >from 5Mhz to 455 Khz. Fresh dry batteries generally are fairly close to their nominal voltages, and an automobile battery that is fully charged is a first cut "standard" 12.6 volts. Accurate voltages above that are hard to find in the basement workshop. Ohmmeters tend to be wildly inaccurate, but you can measure a bunch of resistors of different values to get "somewhere near." (Faq editor note: other countries have frequency-standard time stations; if someone familiar with them could E-mail me the information, I will include it here). The rule of thumb is that two-figure accuracy is readily achievable, and more than what is needed for service work. However, if you are using flea-market test equipment, it may have been discarded or surplussed because it could not be calibrated, or may not have been checked and calibrated for thirty or forty years. Q. I tried to use a Tek scope to trouble-shoot my AC-DC set, but when I connected the probe ground, I got sparks and burned out the wire. What's wrong? A. US AC-DC sets typically have one side of the line connected directly to chassis ground. Some European sets may also have a direct connection between one side of the supply mains and the chassis. Virtually all US test equipment built over the last 40 years uses a three-prong plug with a direct connection between the ground prong and the test equipment chassis. What happened here is that the radio was plugged in with the high side of the line connected to its ground, and you connected the ground strap across the line voltage. While in US power distribution systems, the "neutral" wire is connected to earth ground at the distribution panel, grounding the line neutral at the radio may cause currents to circulate in the neutral-ground circuits (ground loop). The best way to avoid a shock hazard with an AC-DC set is to use an isolation transformer. It is possible, but not recommended, to "float" the test equipment ground by using a two-prong "cheater," but this may cause other problems. Plugging the set in so that the grounded side is neutral may also work, particularly if you use a .01 mfd or larger cap in the ground circuit to the scope. However, with any method other than an isolation transformer, the scope and the radio may have some voltage between them, posing a shock hazard as well as problems making measurements. AC-only sets were often connected with a .02 mfd cap from each side of the AC line to the chassis to provide an AC reference ground between the chassis and the AC line. If either of these capacitors is shorted, the chassis is directly connected to one side of the line. Find these caps and check them before doing any trouble-shooting. Q. I want to fix my old radio myself, and have never used a soldering iron before. What do I need to do? A. All of the manufacturers that use solder to connect electronic components run "solder school" for new employees. Electronics soldering is not the same as soldering pipes in plumbing or doing auto body lead work. There is only one way to learn, and that is to do it. You will need: a. Soldering iron. A Weller or an Ungar "solder station" with a 35-50 watt "pencil" iron and thermal control in a soldering iron holder is best. If you are going to unsolder components directly soldered to a chassis, you will need at least 50 watts, and maybe a larger 100 watt iron. Do yourself a favor and buy a good soldering station. It will cost more than a cheapie Radio Shack iron, but you will find that the tip stays in good condition a lot longer, and that you do much less damage with heat, using a good iron. The solder station holder provides a place to put the iron down that is safe, a real "plus." b. Solder. Kester or similar ROSIN CORE solder is sold specifically for electronic use. It is "eutectic" solder, that is, 37 percent lead, 63 percent tin, which melts at the lowest temperature. Don't use 60-40 plumber's solder, which is 60 percent lead. c. Small tools for use when soldering. You will want some fine point needle nose pliers, some medium point needle nose pliers, and a small set of diagonal cutting pliers. Also, a small screwdriver and a solder "pick" that has a pointed piece on one end and a v-notched piece on the other. Round this out with a solder sucker (a little pump with a high-temperature plastic piece that you can safely shove into hot solder, and a button trigger to trip the pump). Solder "wick" works well, but remember that when you are removing solder from a 1934 radio terminal, you are removing 4 or 5 times the amount of solder used on a modern printed circuit board---use the pump to remove most of the solder and the wick to remove the rest. Tin your new iron, and keep the tip well-tinned at all times. This means keeping a coat of unoxidized solder on the tip. The solder stations come with sponges. Wet the sponge, and wipe the hot iron on it to clean off residue. To tin the first time, just melt some solder on the tip. The rosin in rosin core solder is a mild flux---that is, chemically active to deoxidize and clean the surface so that solder will flow onto it. Wipe the iron back and forth on the sponge to distribute the solder. When properly tinned, the tip should be shiny with fresh solder all around back about half an inch. Keep the tip looking like this, and you'll eliminate half the problems people have when soldering. To remove components, heat the old joint until the solder melts, and remove the solder with the solder sucker. Bend the old component leads back, and slide the lead out. You'll have to keep the joint hot until you've got the bent-over part of the old lead away from the terminal. This sounds easier than it is. You will want to learn to use the solder pick, small screwdriver, and needle-nose pliers on various joints. If the component you are removing is scrap, clipping the lead and leaving a short loose end often makes getting the loop open easier, and once the loop is open, the lead can be removed by pushing the wire through the terminal. Also, using the nippers (carefully!) to nip the wire loop so that it will break often helps when removing components. Watch out what you are heating, and watch out what you are pushing and pulling on. That iron is hot and will burn wire insulation, melt polystyrene (clear plastic coil forms), etc. Move things out of the way so you have a clear shot at the joint you are working on. Don't bend terminals back and forth---they'll break. The worst ones for breaking are on the 7 and 9-pin miniature tube sockets, and if you break one, you get to replace the socket, which is a major task. Coil form terminals are not far behind, and most of those old coils are irreplaceable. The big terminals mounted on phenolic terminal strips are fairly rugged, and components fastened to them are a good place to get some experience before tackling finer work. On fragile terminals, once the solder is removed (use solder sucker and solder will to remove as much as possible), a little judicious use of nippers to cut wires, and other little tricks you will learn as you go along, to avoid any stress on the terminal, is the only way to go. Another trick is to make a cold solder joint. Just wiggle the lead a little while the solder cools, and it will stay free. You can then work with two hands to get the joint opened up and the lead out of the hole. When installing new components, run the leads for all new components going to a particular terminal before soldering any. Form the leads into new loops and nip off the excess. Place the iron against the terminal and melt some new solder by pressing it against both the iron and the terminal. It will melt on the iron first, then into the terminal. Don't use too much solder, and make sure that the solder flows onto all the wires and onto the terminal. Once the solder has flowed into the joint, remove the iron and wait for the joint to cool and solidify. This is where cold solder joints occur. A cold solder joint happens when a lead gets wiggled as the joint is cooling, preventing formation of a solid bond. They are generally easy to see, because the solder ball on the terminal will often be very frosty, and not have a smooth surface. They are also very easy to make, and you should experiment with some scrap---just wiggle the pieces as the solder is cooling, and you'll get a cold solder joint. If you've got any doubt about a joint, reheat it and reflow the solder. While the people who originally built these radios were very skilled, you'll occasionally find a cold solder joint or a joint with no solder at all on a lead that has been there as long as the radios has been around. Don't be afraid to inspect, reheat, and reflow a fifty year old solder joint that looks suspicious just because it has been there for fifty years. There are two schools of thought on rosin removal. You can leave the rosin on the joint, and most radios were made that way. However, if you do want to remove it, isopropyl rubbing alcohol on a Q-tip will melt it right off. -- *********************************************************** Hank van Cleef vancleef@bga.com vancleef@tmn.com ***********************************************************