20070417.ba v04_n041.bam.20070417 >From ???@??? Tue Apr 17 13:07:24 2007 -0500 Date: Tue, 17 Apr 2007 18:06:18 GMT From: Old Tube Radios To: Old Tube Radios Subject: BOATANCHORS digest 4041 Message-Id: <20070417180628.9B22A4700FF@srvr1.theporch.com> BOATANCHORS Digest 4041 Topics covered in this issue include: 1) Re: SX-42 in need of renovation by wb3fau@att.net 2) by jcoward5452@aol.com 3) semi- annual WTB request for Morrow CM-1 case by jcoward5452@aol.com 4) Info? Applied Communications SR-2153 rcvr. by "Art Lebermann" 5) Viking KW question by Jim Garland <4cx250b@muohio.edu> 6) Re: Viking KW question by Rodger 7) Re: Viking KW question by Bob Roehrig 8) Re: Viking KW question additional by Rodger 9) Grungy no more by Robert Nickels 10) Viking KW versions by "James C. Garland" <4cx250b@muohio.edu> 11) Re: Cleaning Variable Caps by "Tom Rauch" 12) Masking lettering by Robert Nickels 13) Re: Masking lettering by Jack Antonio 14) BBC Show On Radio Jamming by Jerry Proc 15) Re: Masking lettering by Jerry Proc 16) Re: Masking lettering by "Arden Allen" 17) RE: Masking lettering by "Ed Sieb" 18) Our Wonderful New "Extra" Class by "David Stinson" 19) Free to good home: TU-6-B by Gary Woods 20) Thanks, need another batch o'reviewers by John Sehring 21) Nat'l NC-2040D - It's alive! by John Sehring ---------------------------------------------------------------------- From: wb3fau@att.net To: Old Tube Radios Cc: "Arden Allen" Subject: Re: SX-42 in need of renovation Date: Tue, 10 Apr 2007 16:11:53 +0000 Message-Id: <041020071611.1938.461BB7490006EB740000079221603762239A0E00CC0D99@att.net> No problem, you put it on Ebay, i assure you, i won't buy it! ------------------------------ To: Old Tube Radios Content-Transfer-Encoding: 7bit Subject: Date: Wed, 11 Apr 2007 00:06:41 -0400 MIME-Version: 1.0 From: jcoward5452@aol.com Content-Type: text/plain; charset="us-ascii"; format=flowed Message-Id: <8C94A05F1971B98-1E3C-5AC7@WEBMAIL-MB17.sysops.aol.com> ________________________________________________________________________ AOL now offers free email to everyone. Find out more about what's free from AOL at AOL.com. ------------------------------ To: Old Tube Radios Content-Transfer-Encoding: 7bit Subject: semi- annual WTB request for Morrow CM-1 case Date: Wed, 11 Apr 2007 00:11:36 -0400 MIME-Version: 1.0 From: jcoward5452@aol.com Content-Type: text/plain; charset="us-ascii"; format=flowed Message-Id: <8C94A06A1DEB008-1E3C-5ADA@WEBMAIL-MB17.sysops.aol.com> Groups, This WTB request is for a decent housing for a Morrow CM-1 Conelrad receiver. Thanks, Jay KE6PPF ________________________________________________________________________ AOL now offers free email to everyone. Find out more about what's free from AOL at AOL.com. ------------------------------ Message-ID: <380-220074311213531406@earthlink.net> From: "Art Lebermann" To: Old Tube Radios Subject: Info? Applied Communications SR-2153 rcvr. Date: Wed, 11 Apr 2007 14:35:31 -0700 MIME-Version: 1.0 Content-type: text/plain; charset=US-ASCII This is not a tube radio, but I'd say that it qualifies for "boatanchor" status. I'm looking for any info you may have for an "Applied Communications" VHF/UHF receiver, model SR-2153. This is a rather large solid-state receiver, rack mount, with keypad entry and digital display. Internal construction with plug-in circuit boards. I'd guess that this receiver was manufactured for Government use - possibly Signal Intelligence? I've done the usual Internet searches, but with no results. Any info, or suggested resources, will be much appreciated. Photos available on request. 73, Art Lebermann W6REQ ------------------------------ Message-Id: <7.0.1.0.2.20070411160751.0234b008@muohio.edu> Date: Wed, 11 Apr 2007 17:04:28 -0700 To: Old Tube Radios From: Jim Garland <4cx250b@muohio.edu> Subject: Viking KW question Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed Hi Gang, I've been reassembling my desk KW pedestal and finally have it back together. That plate xfmr is a back-killer, for sure! Everything seems to work fine, but as long as I have it out of the cabinet I'd like to check the VR tube currents for the screen regulator and RF bias. They are supposed to be in the 20-40 mA range. My amp's layout doesn't seem to quite agree with the photos in the manual. It's s/n 100019. There are two pairs of meter test jacks on the VR tube chassis, one pair for measuring the Screen VR tube current (actually four VR75s in series) and the other for measuring the RF bias VR-tbe (a single VR90). (The schematic shows a normally closed phone-jack for each.) As best I can tell, the VR90 pins on the jack are internally jumpered, possibly with a resistor of a couple tenths of an ohm, and show continuity to ground. The other jack shows an open circuit between the pins and no continuity to ground. It's not easy to measure resistances because the jacks are strange black bakelite things with holes bigger than standard banana plugs. Also, a wiring harness runs in front of them. So Question 1 is: does anybody know how to measure these currents or what's behind the jacks? All the tubes seem to glow, except for one of the VR75s, which is an odd-shaped German tube that looks like a slightly elongated 5Y3. Can one ballpark the current by looking at the glow? Question 2: On the rear panel of the amplifer, just above the power connectors, are four pin jacks, colored Red, Yellow, Black, and White. The Red and Yellow are jumpered and the Black and White are jumpered. The photo in the manual doesn't show any jacks, so I'm wondering what they're for? And Question 3 has nothing to do with Johnson amps, but I'm submitting for a buddy: What is the termination resistance for McCoy xtal filters? I vaguely recall it being 200 ohms, but maybe somebody knows for certain. Tnx and 73, Jim Garland W8ZR ------------------------------ Message-ID: <461D7CD8.7000003@dtnspeed.net> Date: Wed, 11 Apr 2007 19:27:04 -0500 From: Rodger MIME-Version: 1.0 To: Old Tube Radios CC: Old Tube Radios Subject: Re: Viking KW question Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Hi Jim, There were two different versions of the screen regulator circuitry. As I recall, the earliest version did not use a regulator for the bias and selection of which grouping of the 5 tubes used in the screen regulator depended upon the mode selected. The later version made the change to 4 of the tubes being dedicated to the screen and the remaining tube was used to regulate the bias in SSB mode. In the original, 4 of the tubes were VR-150 types and the other was a VR-105. In the later version, a VR-90 is used for bias regulation in SSB but only V202 is a VR-75 and V203-205 are VR-150 tubes so it sounds like your Desk KW is either modified somewhere in between the two circuits or has some incorrect tubes installed. My Desk was the original style but since it was completely disassembled when I bought it I changed it to the "new" style regulator circuitry during restoration. If you have the new style regulator then V202 should only be active in the SSB mode when higher screen voltage is supplied and this tube is a VR-75. During high power AM operation then V203,204, and 205 should be active providing 450 volts. At this point I would pull the regulator tube chassis and check the wiring and the jacks as they should be wired and used as per the diagram. I did make a few changes to my Desk KW: 1. I replaced a badly plated plate relay with a pair of solid state relays mounted on a large heat sink, since my 872 rectifiers had already been replaced with SS units I removed the rectifier filament transformer and this provided a space and pre-drilled holes to mount the relays/heat sink. 2. I added current inrush limiting to help protect the transformers and tube filaments. I used separate devices for the various transformers. By the way, thanks for your Viking 500 article in ER! I used your values during my just completed 500 restoration. 3. I added a small value resistor in series with the screen supply and used the drop across this resistor to drive a small external screen meter. I brought the leads out of the back through an existing opening so no additional holes were needed and the meter is mounted in its own small box. Johnson added a screen metering function to their slightly newer Thunderbolt and it is a good idea for the Desk. I can assure you that tuning up to values in the chart does NOT magically result in the proper screen current for the Desk KW. I have schematics for both versions and I think they are on Bama but if not let me know and I can send you a copy. 73, Rodger WQ9E Jim Garland wrote: > Hi Gang, > > I've been reassembling my desk KW pedestal and finally have it back > together. That plate xfmr is a back-killer, for sure! > > Everything seems to work fine, but as long as I have it out of the > cabinet I'd like to check the VR tube currents for the screen > regulator and RF bias. They are supposed to be in the 20-40 mA range. > My amp's layout doesn't seem to quite agree with the photos in the > manual. It's s/n 100019. > > There are two pairs of meter test jacks on the VR tube chassis, one > pair for measuring the Screen VR tube current (actually four VR75s in > series) and the other for measuring the RF bias VR-tbe (a single > VR90). (The schematic shows a normally closed phone-jack for each.) > As best I can tell, the VR90 pins on the jack are internally jumpered, > possibly with a resistor of a couple tenths of an ohm, and show > continuity to ground. The other jack shows an open circuit between > the pins and no continuity to ground. It's not easy to measure > resistances because the jacks are strange black bakelite things with > holes bigger than standard banana plugs. Also, a wiring harness runs > in front of them. > > So Question 1 is: does anybody know how to measure these currents or > what's behind the jacks? All the tubes seem to glow, except for one > of the VR75s, which is an odd-shaped German tube that looks like a > slightly elongated 5Y3. Can one ballpark the current by looking at > the glow? > > Question 2: On the rear panel of the amplifer, just above the power > connectors, are four pin jacks, colored Red, Yellow, Black, and > White. The Red and Yellow are jumpered and the Black and White are > jumpered. The photo in the manual doesn't show any jacks, so I'm > wondering what they're for? > > And Question 3 has nothing to do with Johnson amps, but I'm submitting > for a buddy: What is the termination resistance for McCoy xtal > filters? I vaguely recall it being 200 ohms, but maybe somebody knows > for certain. > > Tnx and 73, > > Jim Garland W8ZR > > > ------------------------------ Date: Wed, 11 Apr 2007 19:29:23 -0500 (CDT) From: Bob Roehrig To: Old Tube Radios Cc: Old Tube Radios Subject: Re: Viking KW question Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed On Wed, 11 Apr 2007, Jim Garland wrote: > Hi Gang, > > I've been reassembling my desk KW pedestal and finally have it back together. > That plate xfmr is a back-killer, for sure! Sorry I can't answer some of your questions Jim.; I have a desk KW but it has been modified to a G-G linear so there is no modulator or screen/bias supplies left in it. > Question 2: On the rear panel of the amplifer, just above the power > connectors, are four pin jacks, colored Red, Yellow, Black, and White. The > Red and Yellow are jumpered and the Black and White are jumpered. The photo > in the manual doesn't show any jacks, so I'm wondering what they're for? I have no idea. Sounds like a mod somebody added. Bob Roehrig Aurora University Telecom dept. broehrig@aurora.edu K9EUI W9ZGP WD2XSH/19 630-844-4898 fax 630-844-4222 "Nostalgia is a thing of the past" ------------------------------ Message-ID: <461D8266.7040605@dtnspeed.net> Date: Wed, 11 Apr 2007 19:50:46 -0500 From: Rodger MIME-Version: 1.0 To: Old Tube Radios CC: Old Tube Radios Subject: Re: Viking KW question additional Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Jim, If the jacks are like the ones that I have, it is set up sort of like a phone jack where in this case a grounded piece shorts to the "ring" normally. When the plug is pushed in the shorted piece is moved away and the plug makes contact with the ring. I didn't think the shorting was very reliable so I jumpered across them to ensure that the regulator string would be grounded and I used an DVM to measure the resistance and voltage drop across the series dropping resistors to calculate (and accurately set) regulator current. Rodger WQ9E ------------------------------ Message-ID: <461DA4EE.9070500@oneradio.net> Date: Wed, 11 Apr 2007 22:18:06 -0500 From: Robert Nickels MIME-Version: 1.0 To: Old Tube Radios Subject: Grungy no more Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Here's a tip you may want to put in your restoration file. A 30 minute soak in "CLR" - the calcium, lime, rust remover - did an amazing job of removing the surface grunge: see before and after pics: http://smg.photobucket.com/albums/v652/ranickel/Grungy%20Capacitor/ Not perfect, but certainly brought them from grungy up to "typical" condition. Thanks for John Gillespie for this great suggestion. 73, Bob W9RAN ------------------------------ Message-Id: <7.0.1.0.2.20070412154037.024dca18@muohio.edu> Date: Thu, 12 Apr 2007 16:33:36 -0600 To: Old Tube Radios From: "James C. Garland" <4cx250b@muohio.edu> Subject: Viking KW versions Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; format=flowed Hi Gang, Tnx to those who responded with info on different variations of the Viking KW. Here's what I've learned, so far. 1. There are three variations of the Viking KW, with the original circuit diagram dated 7-13-55, and two revisions dated 2-58, and 7-17-62. (There may be more I don't know about.) 2. The first variation (2-58) changed the rf amplifier and modulator bias circuits. Four resistors and a pot in a divider chain were changed. There were changes in the VR Tubes. The original circuit had 4 VR150s and a VR105. In the upgrade, two of the VR150s were changed to VR105s and the original VR105 was changed to a VR90. A VR current adjustment pot also changed value. In the RF deck, the plate coupling caps changed values, as did two of the fixed loading caps. The plate overload relay adjustment pot changed from 50 to 10 ohms. 3. The second variation (7-17-62) changed none of the screen divider resistor values, but one of the VR105s from the previous revision was changed to a VR75, and another of the VR105s was changed back to a VR150, which is what had been there originally. This all resulted in in three VR150s, one VR75, and one VR90. In addition, one of the VR current adjustment pots (R213) changed value. In the RF deck, the 80m input circuit got a new coupling link into the input inductor, instead of sharing the link with the next two higher bands. 4.. Upgrade kits were made available to existing owners through letter dated 2/21/58 to improve SSB operation. The cost was $24 and according to the letter the changes included a. Screen voltage pwr supply changed to provide 510V regulated voltage. b. Bias supply changed to provide -90V (regulated) instead of -100V unregulated. c. Resistor R110 removed from final amplifier grid return. Looking at the pattern of upgrades, it appears that EFJ had some problems optimizing the screen voltages . In order to get it right, they mixed and matched VR tubes in various combinations, and fiddled with values on the screen voltage divider network. My impression is they could have saved themslves some grief had they put a screen current meter in the amp. With no screen current meter, users had to load the amp according to the specified cathode current and hope the screen current was adjusted properly. Bad idea! (Incidentally, the recommended cathode in AM dropped from 490 mA to 470 mA in one of the variations.) If you've got a Viking KW and aren't sure which variation you have, an easy way to tell is by looking at the VR tubes. Here's what to look for: Original (7-13-55) circuit: 4-VR150a, 1-VR105 FIrst revision (2-58): 2-VR150s, 2-VR105s, 1-VR90 Second revision (7-17-62): 3-VR150s, 1-VR75, 1-VR90. Tnx again to the guys who sent me info on this. I'm still not quite sure what's in my amplifier. It seems to be a mix of upgrades and I haven't got them sorted out yet. 73, Jim W8ZR ************************* James C. Garland 102 Spur Ranch Road Santa Fe, NM 87540 www.w8zr.net ************************* ------------------------------ Message-ID: <01a401c77e3d$a4352680$660fa8c0@radioroom> From: "Tom Rauch" To: Old Tube Radios Subject: Re: Cleaning Variable Caps Date: Fri, 13 Apr 2007 22:35:50 -0400 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit Small micro burrs and points often do as much to lower breakdown voltage as naked-eye visible points. The normal polishing procedure of air variables is to first knock the rough edges off and then tumble the plates in Walnut shells for several hours to polish them. Sanding, filing, bead blasting, and even etching can seriously lower the breakdown voltage. Of course pitting can reduce breakdown. A bead blast or etch might be better than a lumpy surface....but none will be anywhere as good as most commercially manufactured variables have when new. If people could have gotten away with a bead blast when manufacturing new caps they would have done that. Of course sometimes something not perfect is better than nothing. Unfortunately it sometimes is worse. I'd bet a rock hound would have something to tumble small plates. 73 Tom ------------------------------ Message-ID: <46211237.1020901@oneradio.net> Date: Sat, 14 Apr 2007 12:41:11 -0500 From: Robert Nickels MIME-Version: 1.0 To: Old Tube Radios Subject: Masking lettering Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Anyone know of a readily-available product that can be used to mask off lettering on a panel for overspraying? I remember some pink latex stuff we used to use on PC boards to keep plated thru holes open, it was like rubber cement that you could pull right off afterward. Wonder if rubber cement might work? I'd like to be able to maks just the lettering, not a big area like I'd get with masking tape. Thanks and 73, Bob W9RAN ------------------------------ Message-ID: <46211F68.7070303@sbcglobal.net> Date: Sat, 14 Apr 2007 11:37:28 -0700 From: Jack Antonio MIME-Version: 1.0 To: Old Tube Radios CC: Old Tube Radios Subject: Re: Masking lettering Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit There was a product modelers used called Liquid Mask, or Magic Mask, or something like that, mainly used to mask off clear plastic canopies prior to spray painting. Try the local hobby store. Haven't built a model airplane in years, so don't know if it still available. Jack Jack Antonio WA7DIA scr287@sbcglobal.net Robert Nickels wrote: > Anyone know of a readily-available product that can be used to mask off > lettering on a panel for overspraying? I remember some pink latex stuff > we used to use on PC boards to keep plated thru holes open, it was like > rubber cement that you could pull right off afterward. Wonder if rubber > cement might work? I'd like to be able to maks just the lettering, not > a big area like I'd get with masking tape. > > Thanks and 73, > Bob W9RAN > > ------------------------------ Date: Sat, 14 Apr 2007 15:27:54 -0400 (EDT) From: Jerry Proc Subject: BBC Show On Radio Jamming To: Old Tube Radios MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Message-ID: <660141.12437.qm@web90608.mail.mud.yahoo.com> Hello Everyone, This extract from the Royal Naval Amateur Radio Society Sunday News. *************** BBC Radio 4 programme on Jamming On Wednesday 18th April BBC Radio 4 1330-1400 UK time "It's My Story: Political Interference" The end of WW2 saw Soviet bloc radio engineers working to jam radio signals coming from the West. This lasted for nearly 40 years, with the Western engineers doing their best to beat the jamming. In this programme, Roger Bolton talks to engineers from both sides and learns what happened when the jamming eventually stopped. The programme will also be available on line via the "Listen Again" facility. See: http://www.bbc.co.uk/radio4/ -- Regards, Jerry Proc E-mail: jerry7proc@yahoo.com Be smarter than spam. See how smart SpamGuard is at giving junk email the boot with the All-new Yahoo! Mail at http://mrd.mail.yahoo.com/try_beta?.intl=ca ------------------------------ Date: Sat, 14 Apr 2007 16:45:10 -0400 (EDT) From: Jerry Proc Subject: Re: Masking lettering To: Old Tube Radios MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Message-ID: <663550.71040.qm@web90615.mail.mud.yahoo.com> Hi Bob, Another idea is to visit an automotive paint supplier and see what products they have for masking small areas prior to painting. Also I hope you realize that unless you match the paint perfectly in both colour and lustre, you will end up with a visible rectangle of origianal paint at each place where the lettering has been masked off. Is that a problem for you? Alternate suggestion: Paint over the entire panel, then use a Brother 'P' Touch label maker using either black or white transparent tape to make new lettering. The tape can be trimmed to as narrow as 3/16 inch. An example of this techique can be found on my AN/SRC-501 radio mockup on document: http://www.jproc.ca/rrp/rr4desc.html At several feet away, its hard to discern that the lettering is on transparent tape. Here's an old navy trick used during spray repainting. For any item which needs to be protected, apply a generous coat of Vaseline over it. When the paint dries, just wipe off the Vaseline. I don't know if this is a suitable technique for a front panel. --- --- Robert Nickels wrote: > Anyone know of a readily-available product that can > be used to mask off > lettering on a panel for overspraying? I remember > some pink latex stuff > we used to use on PC boards to keep plated thru > holes open, it was like > rubber cement that you could pull right off > afterward. Wonder if rubber > cement might work? I'd like to be able to maks just > the lettering, not > a big area like I'd get with masking tape. > > Thanks and 73, > Bob W9RAN > > -- Regards, Jerry Proc E-mail: jerry7proc@yahoo.com Get news delivered with the All new Yahoo! Mail. Enjoy RSS feeds right on your Mail page. Start today at http://mrd.mail.yahoo.com/try_beta?.intl=ca ------------------------------ Message-ID: <004c01c77ed6$eda71640$eae47443@KB6NAX> From: "Arden Allen" To: Old Tube Radios Subject: Re: Masking lettering Date: Sat, 14 Apr 2007 13:52:08 -0700 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit > ...Wonder if rubber > cement might work? ....... No! The solvent in rubber cement will likely damage the lettering paint. Here's an idea: Mask over the lettering with Scotch Magic Tape. With a slightly dull X-acto knife trim the tape to size around the lettering. Practice getting the feel for how much pressure it takes to cut the tape without scoring the paint on the panel. Arden Allen KB6NAX ------------------------------ From: "Ed Sieb" To: Old Tube Radios Subject: RE: Masking lettering Date: Sat, 14 Apr 2007 17:36:00 -0400 Message-ID: MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit What you want is "Frisket" available at sign shops and art supply houses. http://www.google.com/search?hl=en&q=Frisket Ed, VA3ES ------------------------------ Message-ID: <000801c78023$b758a880$fa01fea9@Default> From: "David Stinson" To: Old Tube Radios Subject: Our Wonderful New "Extra" Class Date: Mon, 16 Apr 2007 07:35:27 -0500 MIME-Version: 1.0 Content-Type: text/plain; charset="Windows-1252" Content-Transfer-Encoding: 7bit Heard yesterday on 75 meters, new "Extra" section. This is a word-for-word quote (no; it's not a joke): "I got a Siltronix; if I get the right slider, I can slide it on down to 75 meters, I think." "Yep; that's a good radio for sliding, but they do got a lot of bleed-over." "Yeah; them Siltronix sure will bleed..." ....... sigh..... ------------------------------ From: Gary Woods To: Old Tube Radios Subject: Free to good home: TU-6-B Date: Mon, 16 Apr 2007 11:02:38 -0400 Message-ID: <4s3723lsl4dbe3qma1pog3uhal41lkv383@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit This is not a "Rare Bird." It isn't even complete, missing the PA tuning cap and coupling switch. MO tuning and bandswitch mechanicals, coil and cap are there, but internal wiring mostly diked out. Anybody want this for shipping? There's currently a loon or loon making weird off-topic posts to many newsgroups often forging a regular sender, but with followups set to news.admin.net-abuse.email, so unwitting dupes bomb that group with their replies. Whenever a strange post shows up, it's a good idea to see where it's cross-posted or where the followups will go. Gary Woods O- K2AHC Public keys at www.albany.net/~gwoods, or get 0x1D64A93D via keyserver gwoods@albany.net gwoods@wrgb.com fingerprint = E2 6F 50 93 7B C7 F3 CA 1F 8B 3C C0 B0 28 68 0BB 3C C0 B0 28 68 0B ------------------------------ Content-Disposition: inline Content-Transfer-Encoding: binary Mime-Version: 1.0 From: John Sehring To: Old Tube Radios Subject: Thanks, need another batch o'reviewers Content-Type: text/plain Message-Id: <20070417160827.51C773011C9@filter6.e-filtering.net> Date: Tue, 17 Apr 2007 10:08:27 -0600 (MDT) I got some excellent feedback on my antenna in the trees manuscript from BA readers. Did I expect anything less?! I'm continuing to work on it & will run much-revised art. past folks again, if they like. I have another manuscript ready, on a totally different subject, of especial interest I think to the BA crowd: An AM modulation scheme for reducing the effects at the receiver of selective fading caused by multipath propagation. Pse email me directly if interested, thanks. --John Sehring WB0EQ/VE6 ------------------------------ Content-Disposition: inline Content-Transfer-Encoding: binary Mime-Version: 1.0 From: John Sehring To: Old Tube Radios Subject: Nat'l NC-2040D - It's alive! Content-Type: text/plain Message-Id: <20070417180602.8FEF834D339@filter6.e-filtering.net> Date: Tue, 17 Apr 2007 12:06:02 -0600 (MDT) Well, after long & gentle resucitation, my National NC-2-40D is alive! I used a long, slow process to get there. Got lots of tips from you folks on this. Thanks! 1. All tubes removed but pilot lites left in. B+ applied from ext. supply throught large resistor to get current limiting (in case of problems), monitored B+ voltage & current. Voltage applied slowly, up to rated B+ of radio. Looked for 1) bad eletrolytic caps in HV supply or choke problems, 2) bad bypass caps. Latter would draw some leakage current & pull down voltage via resistors feeding the bypass. VTVM & fingertips can sniff 'em out. Noticed no spikes in current drawn as B+ came up. Paused at 25, 50 & 75% of rated B+ to ck things. Let radio cook a long time at each level of B+. 2. B+ supply disconneced. Measured resistance from all windings of xfmr to each other & ground to look for goofy readings. 3. Applied AC slowly, paused at about 25, 50 & 75%, then up to 115 VAC via variac to ck out power xfmr & AC wiring. Pilot lamps glowed, good sign! I coulda had a small light bulb in series with the radio for this. 3A. Repeated 3 above with rectifier tube installed. Monitored & limited B+, it could go sky high w/o load of tubes in radio. 4. Cked all tubes, found one w/dead short, replaced it, installed all tubes. Hooked up external spkr/output xfmr to radio. 5. Applied AC again via variac, brought it up slowly. Radio now perking along nicely, listening to Radio Taiwan on 49 m in evening. Radio still has scratchy controls, is on the weak side but everything works, is vy stable, selective & has beautiful recovered audio quality, nicest I've heard! Must be combo of that low-distortion infinite impedance detector & push-pull 6V6's & good qual. speaker. I'm impressed. The band coil change mechanism reminds me of a beautiful antique engine. Radio does have a strange AVC detector ct, need to think about that some more, uses a 6V6! --John Sehring WB0EQ/VE6 ------------------------------ End of BOATANCHORS Digest 4041 ******************************