20070226.ba v04_n019.bam.20070226 >From ???@??? Mon Feb 26 02:08:07 2007 -0600 Date: Mon, 26 Feb 2007 08:07:07 GMT From: Old Tube Radios To: Old Tube Radios Subject: BOATANCHORS digest 4019 Message-Id: <20070226080709.0D547187AFD@srvr1.theporch.com> BOATANCHORS Digest 4019 Topics covered in this issue include: 1) Re: Solid State Rectifier Replacement for 51JX by wb3fau@att.net 2) Re: Solid State Rectifier Replacement for 51JX by Steve Berg 3) National R1230/FLR Receiver by Jerry Proc 4) Re: Solid State Rectifier Replacement for 51JX by Dan Arney 5) Re: Solid State Rectifier Replacement for 51JX by "Tom Rauch" 6) Re: Solid State Rectifier Replacement for 51JX by "Tom Rauch" 7) RE: Solid State Rectifier Replacement for 51JX by "Thomas Frobase" 8) Re: Solid State Rectifier Replacement for 51JX by "Tom Rauch" 9) RE: Solid State Rectifier Replacement for 51JX by "Rodger" 10) FW: Solid State Rectifier Replacement for 51JX by "Thomas Frobase" 11) Re: Solid State Rectifier Replacement for 51JX by "David Stinson" 12) Re: Solid State Rectifier Replacement for 51JX by "Tom Rauch" 13) Re: Solid State Rectifier Replacement for 51JX by "Tom Rauch" 14) Re: Solid State Rectifier Replacement for 51JX by "Tom Rauch" 15) Re: Solid State Rectifier Replacement for 51JX by "Morris Odell" 16) Re: Solid State Rectifier Replacement for 51JX by "Arden Allen" ---------------------------------------------------------------------- From: wb3fau@att.net To: Old Tube Radios Cc: "Arden Allen" Subject: Re: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 19:39:25 +0000 Message-Id: <022520071939.14464.45E1E5ED0003F2040000388021602807419A0E00CC0D99@att.net> I agree with you Arden. I have 5R4s in the Heath Apache, They handle the inrush- overload so well. I can see some initial internal arcing on a cold start, but they work. Russ. ------------------------------ Message-ID: <45E1E974.9060303@tbc.net> Date: Sun, 25 Feb 2007 13:54:28 -0600 From: Steve Berg MIME-Version: 1.0 Cc: Old Tube Radios Subject: Re: Solid State Rectifier Replacement for 51JX Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit To: Old Tube Radios I have a 5R4 in my P&H 6-150 transverter. I bought the unit used when I was in high school and it has seen considerable use since. I have replaced the final amplifier tube once and the 6CX8 oscillator tube once, but the rest keep chugging along. I have long since stopped putting in solid state rectifiers in old gear that did not come uquipped with them. Might the inrush limiters still be a good idea in older stuff, es[pecially those where sand state diodes came with the unit? Steve WA9JML ------------------------------ Date: Sun, 25 Feb 2007 14:58:54 -0500 (EST) From: Jerry Proc Subject: National R1230/FLR Receiver To: Old Tube Radios MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Transfer-Encoding: 8bit Message-ID: <187724.42792.qm@web90606.mail.mud.yahoo.com> Hello Everyone, I have just received confirmation that the National R1230/FLR receiver was used in Canadian SIGINT service. As a result I have built a web document for it. http://jproc.ca/rrp/r1230.html I am looking for confirmation on two pieces of information: 1) What is the bandwidth of this wideband receiver? 2) Approximately when was it introduced into service? -- Regards, Jerry Proc E-mail: jerry7proc@yahoo.com __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com ------------------------------ Message-ID: <45E1F76B.8060109@pacbell.net> Date: Sun, 25 Feb 2007 14:54:03 -0600 From: Dan Arney MIME-Version: 1.0 To: Old Tube Radios CC: Old Tube Radios , Arden Allen Subject: Re: Solid State Rectifier Replacement for 51JX Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Arden, Right on OM, Why do these guys have to try and re-engineer something that works fine as designed. THEY ARE ALL TRYING TO PICK THE FLY SPECKS OUT OF THE BLACK PEPPER. They are probably misplaced audio phooollllss!!!. Hank KN6DI ------------------------------ Message-ID: <05d901c7591f$309f6840$640fa8c0@radioroom> From: "Tom Rauch" To: Old Tube Radios Cc: "Old Tube Radios" Subject: Re: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 15:54:36 -0500 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=response Content-Transfer-Encoding: 7bit >I have a 5R4 in my P&H 6-150 transverter. I bought the >unit used when I was in high school and it has seen >considerable use since. I have replaced the final >amplifier tube once and the 6CX8 oscillator tube once, but >the rest keep chugging along. I have long since stopped >putting in solid state rectifiers in old gear that did not >come uquipped with them. Might the inrush limiters still >be a good idea in older stuff, es[pecially those where sand >state diodes came with the unit? Steve, Since I always like to actually measure things when making changes, I sometimes develop a different opinion than common street opinion. I've found the transformers in the gear I've looked at already had more than enough internal resistance to limit current to very safe values upon turn on or warm up. The only exception has been in series connected heater strings that often have one or two tubes take the brunt of warm-up heater dissipation, like the 35Z3 or 50L6 in an "all American five" AC/DC radio. Of far more concern are the slightly high voltages caused by loss of the voltage drop across a high vacuum rectifier or excessive primary voltage. Neither of those issues are cured by current limiting through a step start. I've designed dozens of high power amps and looked at inrush in them also, and unless the filament circuit is foolishly designed with oversized wiring and components most of them are very safe also. Bringing a25-100uF up from zero to several thousand volts is another story. While rectifiers and other components usually handle the surge fine, starts can be very tough on switching systems like relay contacts or power switches. But the very important distinction between systems like that and a low power transmitter or receiver is the amount of energy required to bring the capacitors up, and the very low design ESR of high power transformers used in capacitor input supplies in high power high voltage gear. A typical 3kW 4000 volt supply might have an ESR of ten ohms dumping current into filter capacitors with only a few ohms of resistance, so surge currents might go right to the limits of the power mains for a few cycles without inrush limiting. Most power transformers for rigs we use are in the few dozens of ohms (or higher) , and the supply voltage is only hundreds of volts. You're very unlucky if the current exceeds 1/2 amp or more on inrush. Ohm's Law really saves us in the case of parallel heaters or low power supplies, especially those with chokes. Excessive primary or B+ voltage is another story, and is always worth looking at. It is also not cured by step starting. 73 Tom ------------------------------ Message-ID: <05f801c75920$1f4639b0$640fa8c0@radioroom> From: "Tom Rauch" To: Old Tube Radios Cc: "Old Tube Radios" , "Arden Allen" Subject: Re: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 16:01:15 -0500 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=response Content-Transfer-Encoding: 7bit > Arden, Right on OM, Why do these guys have to try and > re-engineer something that works fine as designed. > THEY ARE ALL TRYING TO PICK THE FLY SPECKS OUT OF THE > BLACK PEPPER. Now fellas, Ward Clever would have something to say about being so rough. There isn't anything wrong with playing around with a radio, that's 99% of the fun. Of course at some point we should gently encourage thinking a problem through and making some measurements, but I've certainly made my share of worthless experiments over the years. If I never tried anything useless I'd never know what useless was. 73 Tom ------------------------------ From: "Thomas Frobase" To: Old Tube Radios Subject: RE: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 17:00:17 -0600 Message-ID: <084401c75930$b8a82cc0$0c01010a@tfrobase1> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Well, I guess I should have just kept to the demise of ham radio "They are probably misplaced audio phooollllss!!!" Thanks for the great technical response Hank. I live in south Texas, try as it might, the air-conditioning here works hard to keep up. Removing the rectifier keeps the radio cooler. I hope we all agree that a cooler radio has a better chance of a longer life, but I guess that is another of my audio phool concepts. Phil at fair radio say's the biggest single request he has for 51Jx radio's is power transformers which are "un-obtainable" So if I lower the current by 3.5 - 5 watts by not using the 5 volt filament it is a start. The downside is when B+ is applied from the solid state rectifier it beats the crap out of the S meter while the tubes in the bridge circuit are warming up. My goal was to add the mod where I did not have to modify the radio, either in the AC primary or otherwise. I guess if I were to suggest a thermal time delay tube it would have been OK, I have seen quite a few R-390A's modified in this manner. I guess my other issue is I am an inbetweener, I am old enough to have worked on tubes and young enough (at least in my mind) to know how to do things differently. So I guess that make me an audio Phooollll, just so you know Dan, I can admit I paid my way through college fixing McIntosh's and I don't mean the computer. But if it helps you Hank, I can't hear a bit of difference in the audio between the 5R4 and a pair of silicon rectifier's and I have been known to use Chinese 12AX7A's on occasion. So in summary, my goal was to find a way to not modify my radio, lower the amount of heat generated, lower the current consumed, keep the meter from beating it self to death and accomplish the task with the minimum amount of components, shame on me for asking this groups opinion. Maybe this is what is wrong with Ham radio today? ... tom< N3LLL -----Original Message----- From: owner-boatanchors@theporch.com [mailto:owner-boatanchors@theporch.com] On Behalf Of Dan Arney Sent: Sunday, February 25, 2007 2:54 PM To: Old Tube Radios Cc: Old Tube Radios; Arden Allen Subject: Re: Solid State Rectifier Replacement for 51JX Arden, Right on OM, Why do these guys have to try and re-engineer something that works fine as designed. THEY ARE ALL TRYING TO PICK THE FLY SPECKS OUT OF THE BLACK PEPPER. They are probably misplaced audio phooollllss!!!. Hank KN6DI ------------------------------ Message-ID: <061f01c75935$be864dc0$640fa8c0@radioroom> From: "Tom Rauch" To: Old Tube Radios Subject: Re: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 18:36:04 -0500 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit > Removing the > rectifier keeps the radio cooler. I hope we all agree > that a cooler radio > has a better chance of a longer life, but I guess that is > another of my > audio phool concepts. That's a fair concept. However, let's look at the real system. > Phil at fair radio say's the biggest single request > he has for 51Jx radio's is power transformers which are > "un-obtainable" So > if I lower the current by 3.5 - 5 watts by not using the 5 > volt filament it > is a start. Off the cuff that sounds good, but the transformer filament power does NOT directly translate into transformer heat. The amount of additional heat would actually be somewhat less than the difference in filament no load to full load voltage times the filament current. If we yank the rectifier tube out and the 5 volt winding goes up to 5.5 volts, and if the current is 2 amps, the dissipation (heat) in the transformer from the tube rectifier is a roaring one watt or less! The heat in the rest of the radio actually doesn't decrease much either. While the actual anode power dissipation represents heat that is reduced, replacing the rectifier with a solid state rectifier simply increases the supply voltage and the dissipation in all the other components. If we add a resistance to bring the voltage back to normal, we now have exactly the same heat again. So the only real heat saving is the filament heat, which is around 10 watts. 10-12 watts out of the entire amount of heat produced in the radio, with virtually none of that heat in the transformer, isn't likely to do much. > The downside is when B+ is applied from the solid state > rectifier it beats > the crap out of the S meter while the tubes in the bridge > circuit are > warming up. My goal was to add the mod where I did not > have to modify the > radio, either in the AC primary or otherwise. I guess if > I were to suggest > a thermal time delay tube it would have been OK, I have > seen quite a few > R-390A's modified in this manner. Because we see it doesn't make it a good mod. If someone really wanted to improve life they should fuse the transformer very close to the fuse limit and lower the primary voltage from the mains. Lowering the primary voltage results in something more than 1:1 and less than 2 for 1 improvement in dissipation. 10% less voltage is generally around 15% less heat. (The load isn't a linear resistance.) Compare that with a 11 to 12 watt drop in heat out of all the power dissipated in the radio, with virtually NONE of the heat in the transformer, and we see why the rectifier substitution is not really as effective as we imagine. As for slamming the meter, that's a good place for a diode clamp! :-) 73 Tom ------------------------------ From: "Rodger" To: Old Tube Radios Subject: RE: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 18:14:27 -0600 Message-ID: <000201c7593b$145fe580$ce01640a@D1JXNQ31> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable Just a short addition to Tom's comments: It would also be useful to = know if there is a common failure mode for the 51J series power transformer and = if so what is the reason for the failure. If it is like the Hallicrafters HT-37 where there appears to be a problem with the 5 volt rectifier = winding leaking/shorting to ground due to the additional DC voltage imposed upon = it then a solid state replacement would help since the high voltage should = then be removed from this winding. Otherwise the heat reduction is small = though for a receiver transformer the rectifier filament is often a significant portion of the total transformer load. One of the saddest transformer failures I have seen was the low voltage unit in a Valiant that I fixed = for a friend many years ago. The early production Valiants were built with standard hookup wire from the low voltage transformer (which supplies = the 866A heaters) to the 866A sockets; of course this wire also has the DC = plate voltage imposed upon it. Arcing and shorting to ground is common, particularly as this wire ages and the result is a dead LV transformer. This particular unit had solid state rectifiers installed in the HV = section but the owner left the heater wiring intact; unfortunately Murphy did = not leave the insulation or the LV transformer intact. 73 Rodger WQ9E ------------------------------ From: "Thomas Frobase" To: Old Tube Radios Subject: FW: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 18:41:24 -0600 Message-ID: <088201c7593e$d9325f70$0c01010a@tfrobase1> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit I still had the meters on to test with, 240 VDC vs. 255 VDC = 15 volts differential times current with the higher voltage 130 Ma = ~ 2 watts more internal dissipation. So one would guess that 15 volts @ 130 MA had to be dissipated somewhere, my guess, the rectifier tube. So in reality the 2 watts are distributed through the radio. My point earlier, all be it not explained well, the rectifier generates a lot of heat in a 51J it is right next to the transformer. If one would take a rough estimate of the power drawn from the transformer B+ .130 ma X 255 = 34 watts Filaments 5.25 amps X 6.3 volts = 34 watts Rectifier 2 amps X 5.0 volts = 10 watts --------------------------------------------------- 78 watts Without the rectifier -10 watts --------------- 68 watts = 13 % savings without the rectifier ------------------------------ Message-ID: <004201c7593f$3c8661c0$fa01fea9@Default> From: "David Stinson" To: Old Tube Radios Subject: Re: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 18:44:11 -0600 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit I recently restored a nice National comm receiver. The rectifier was the usual full-wave with center tap to ground. I removed one of the B+ transformer leads and connected the remaining to both plates of the rectifier, making it a half-wave rectifier and dropping the plate voltage considerably. Don't remember now, but seemed it was something like going from +250 volts down to +110 volts. No noticable hum, very little loss of volume and a cooler, quicker to stablize radio was the result. I left it that way and the new owner did, as well. 73 Dave S. ------------------------------ Message-ID: <064501c75945$9e33f850$640fa8c0@radioroom> From: "Tom Rauch" To: Old Tube Radios Subject: Re: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 20:29:43 -0500 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit > I removed one of the B+ transformer leads and connected > the > remaining to both plates of the rectifier, making it a > half-wave > rectifier and dropping the plate voltage considerably. ....but all of that drop is no different than adding a dropping resistor. Now all of the heat that could have been split between both sides of the transformer is concentrated in half of the secondary winding, so the only half the transformer secondary winding becomes the dropping resistance and dissipates all the heat. ALL of the additional voltage drop comes at the expense of additional heat, and all of the heat is one half the winding area. Not good. With a full wave 5Y3 tube rectifier assuming 250V RMS 100 ohm ESR secondary and a 5000 ohm load, the transformer RMS secondary current is around 62mA RMS Changing the same transformer to a half wave solid state now changes the ESR to 200 ohms and the RMS current in the half-winding to 130mA. The fact it works is a testimony to how conservative the transformer was built! It would be a whole lot easier on the transformer if the heat was moved outside the transformer to a resistor. 73 Tom ------------------------------ Message-ID: <064e01c7594c$02312430$640fa8c0@radioroom> From: "Tom Rauch" To: Old Tube Radios Subject: Re: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 21:15:26 -0500 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit > I still had the meters on to test with, 240 VDC vs. 255 > VDC = 15 volts > differential times current with the higher voltage 130 Ma > = ~ 2 watts more > internal dissipation. So one would guess that 15 volts @ > 130 MA had to be > dissipated somewhere, my guess, the rectifier tube. So in > reality the 2 > watts are distributed through the radio. This is actually an interesting exercise. It seems very strange the voltage only changed 15 volts from a tube to solid state rectifiers. Most receivers I have measured change 40-70 volts on the HV. Is that a capacitor input? And is the capacitor on the input good? I just can't understand such a small HV change . 73 Tom ------------------------------ Message-ID: <067201c75951$71a4d780$640fa8c0@radioroom> From: "Tom Rauch" To: Old Tube Radios Subject: Re: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 21:54:21 -0500 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=original Content-Transfer-Encoding: 7bit be removed from this winding. Otherwise the heat reduction is small though for a receiver transformer the rectifier filament is often a significant portion of the total transformer load. >> The problems are: 1.) The vacuum tube normally drops significantly more voltage than a solid state rectifier. When we solid state the B+ goes up. That increases heat in the rest of the radio. 2.) The transformer is really pretty efficient with most of the heat related to the poor power factor of the load on the HV winding. Removing a 10 watt resistive load on a filament winding does NOT remove 10 watts of transformer heat. That winding is normally at 90% efficiency or so. Removing a ten watt purely resistive load typically removes about 1 watt of heat from inside the transformer. 3.) Loss of filament power will remove 11 watts of heat inside the cabinet, but only a very small amount of that thermal energy heats the transformer. Most vents right out. 4.) When the rectifier is "harder", the power factor of the load actually increases. (This assumes the load is a capacitor input.) Power factor just kills a transformer. 5.) There is some heat removed by eliminating dissipation in the anodes of the rectifier tube, but if we keep the same HV it just means the dissipation elsewhere must increase the same amount. Things are never anywhere as good as we assume when we make this change. The one very valid point is the filament winding shorting to ground. 73 Tom ------------------------------ Message-ID: <003f01c75974$754c6dd0$ad00a8c0@Morris1> From: "Morris Odell" To: Old Tube Radios Subject: Re: Solid State Rectifier Replacement for 51JX Date: Mon, 26 Feb 2007 18:05:12 +1100 MIME-Version: 1.0 Content-Type: text/plain; format=flowed; charset="iso-8859-1"; reply-type=response Content-Transfer-Encoding: 7bit >> I removed one of the B+ transformer leads and connected the >> remaining to both plates of the rectifier, making it a half-wave >> rectifier and dropping the plate voltage considerably. > > ....but all of that drop is no different than adding a dropping resistor. > Now all of the heat that could have been split between both sides of the > transformer is concentrated in half of the secondary winding, > It would be a whole lot easier on the transformer if the heat was moved > outside the transformer to a resistor. Another problem can arise with the dc component in the transformer secondary due to the half wave rectifier. This can saturate the core leading to even HIGHER primary current. I have a couple of radios whose power supplies have been solid stated for various reasons and they work very well. My R390A suffered a 26Z5 failure with an open heater. I couldn't find a replacement so installed diodes and a dropping resistor in series to give the same B+. The Halli S27 I listen to FM on had its power xfmr replaced by a previous owner and all he could find was one with no 5 volt winding. The 5Z3 is still there for appearance but the real work is done by a couple of diodes and a dropping resistor. I have never experienced any secondary failures because of these mods. Theoretically the resistor dissipates pretty well the same power the tube plates would have done. All you save is the rectifier heater power which probably saves the planet quite a bit of CO2 over 100 years ;-) In radios with directly heated rectifiers (not the case in the 51Jx though) there's still a voltage surge as the rectifier heats up faster than the rest of the tubes. Solid stating then should be no problem as long as enough resistance is added to keep the B+ in spec. 73 de Morris VK3DOC ------------------------------ Message-ID: <003101c7597a$13a80890$d2e47443@KB6NAX> From: "Arden Allen" To: Old Tube Radios Subject: Re: Solid State Rectifier Replacement for 51JX Date: Sun, 25 Feb 2007 23:45:18 -0800 MIME-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Tom is making some good points I'm adding a teency comment or two to: > The problems are: > > 1.) The vacuum tube normally drops significantly more > voltage than a solid state rectifier. When we solid state > the B+ goes up. That increases heat in the rest of the > radio. A silicon diode will drop no more than approximately 1 volt. A high vacuum rectifier will drop up to several tens of volts depending on the current it has to handle. The higher the current the worse the plate efficiency also. So yes, a high vacuum rectifier adds heat load to equipment which can raise internal temperatures in a tightly packed and/or poorly ventilated assemblage. Increasing heating in the rest of the receiver and working power supply components harder obviously gains nothing. Adding some series resistance to keep the B+ down to the same value as produced from a tube rectifier is the sensible answer. It has been believed by some that B+ is harmful to cold tubes but experience has shown that the effect is neglible at the lower voltages receivers typically run on. However delaying B+ application to keep voltages from soaring to considerably higher values before tubes warmup may be a good measure to protect electrolytic capacitors that have insufficient voltage rating. > 2.) The transformer is really pretty efficient with most of > the heat related to the poor power factor of the load on the > HV winding. Removing a 10 watt resistive load on a filament > winding does NOT remove 10 watts of transformer heat. That > winding is normally at 90% efficiency or so. Removing a ten > watt purely resistive load typically removes about 1 watt of > heat from inside the transformer. The power transformers in consumer goods quality ham receivers are typically not very efficient. Some power transformers are so marginal in design they have been known to fail from thermal runaway when operating from high line voltage. Physical size and cost are the controlling factors. Designs that run much cooler have more and/or better iron and larger diameter wire to reduce losses. I'd expect efficiencies considerably worse than 90% in some gear (the 51J receivers, if I've got my hat on right, were somewhat cost constrained commercial designs - I have a 51J4 which needs to be brought to life carefully before I can make any statements about its transformer's efficiency). Power transformers will fail when subjected to overload by worn out high leakage filter caps. The best protection for a power transformer in vintage equipment is the elimination of faulty components down stream. > 3.) Loss of filament power will remove 11 watts of heat > inside the cabinet, but only a very small amount of that > thermal energy heats the transformer. Most vents right out. When components are tightly packed together radiant heating of adjacent components occurs. The ten plus watts of heat coming from a tube rectifier can warm things up. However in my experience most of the heat transformers endure is due to losses in the transformer. > 4.) When the rectifier is "harder", the power factor of the > load actually increases. (This assumes the load is a > capacitor input.) Power factor just kills a transformer. Stated another way, the higher capacitor charging impulse currents increase heating in the transformer while the average delivered current may remain the same if moderated by adding series resistance downstream. However I disagree that the increased heating effect is sufficient to overstress the transformer unless an audiphoole joker hugely increases the filter capacitance, an atrocity commonly done to vacuum tube audio amps. > 5.) There is some heat removed by eliminating dissipation in > the anodes of the rectifier tube, but if we keep the same HV > it just means the dissipation elsewhere must increase the > same amount. The "hardness" of a vacuum tube rectifier generally refers to the quality of vacuum. A softer tube will have a lower plate resistance. A gassy rectifier will create all kinds of mischief if not replaced. > Things are never anywhere as good as we assume when we make > this change. > The one very valid point is the filament winding shorting to > ground. And here we come to the real reason most transformers fail. They simply wear out. The stresses of heat and voltage degrade insulation until there is eventually a breakdown between windings or to the core. Hi-pot testing does not discover all manufacturing defects so some transformers have their failure predetermined by quality problems. Heating is unavoidable in cheap transformers so it's only a matter of time. Arden Allen KB6NAX ------------------------------ End of BOATANCHORS Digest 4019 ******************************