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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
I have no proof of this but I think the original transformers were simply poorly constructed, meaning the original supplier (Stancor ,or other manufacturer of the time) just didn't do a very good job insulating the filament winding.?
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A great many of them had this problem and a great many of those were "fixed" by just pulling the rectifier tube and replacing it with either individual diodes or a module.? Mine has the module that just plugs into the original tube socket.? It's been that way as long as I have had it (probably 15 years or so) with no more problems.
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The corona issue might have been a separate problem,? but it appears that whatever they did to "fix" that didn't fix the poor insulation.
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In my opinion, the best final fix is to get the high voltage DC off that winding.?
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I suspect PW Dahl did know about the "problem" and more than adequately addressed insulating the winding so the Hammond transformers are also probably? just fine.?????
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Now, having said that, if I were to replace my transformer, I would leave the Si diodes in there and if the voltage ended up a little too high, I would use an FET regulator.
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On Tue, Jul 16, 2024 at 06:22 PM, Paul Christensen wrote:
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
¿ªÔÆÌåÓýJust me but I dislike SS rectifier replacements for several reasons.? To deal with the HV to filament winding problem, a new PW Dahl-designed Hammond transformer was recently ordered for my HT-37. ?Although there¡¯s no proof, I must believe that Dahl knew how to design a transformer with adequate winding isolation. ? Paul, W9AC ? From: [email protected] <[email protected]> On Behalf Of Rick W4XA
Sent: Tuesday, July 16, 2024 9:06 PM To: [email protected] Subject: Re: [HallicraftersRadios] HT-37 transformer failure due to rapid STBY-->OFF-->STBY ? My plan would be to replace the tube rectifiers with diodes anyway.? ? -- 73/Rick |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
My plan would be to replace the tube rectifiers with diodes anyway.?
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
Tube Rectifier Compatibility Chart attached.
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
On Tue, Jul 16, 2024 at 01:43 PM, Jim Whartenby wrote:
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The voltage drop afforded with certain tube rectifiers is definitely a factor for low B+ voltage levels.? It's the main problem in the Johnson Valiant.? (Low B+ should be around 300V and many measure a little less than 400V)
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An advantage of freeing up a 5V filament winding is that one can then use it to "buck" the primary so as to accommodate increased AC line voltage.? (I don't have enough auto-transformers [VARIAC's] to go around!)
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If the "low" b+ is still too high then an FET "HV" regulator can be a pretty good option.??
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The? voltage drop with HV rectifiers such as the 866A (according to the data sheet) isn't much and doesn't seem to be as much of a? problem.? But with the 5U4 and other low voltage "diode" valves, it's significant.?
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
¿ªÔÆÌåÓýRick , Re ??Disc ceramic caps shorting would seem rare but you never really know what a 60+ year old part will do! ? the judicious use of fuses even buried inside can mitigate a small failure from escalating to a major disaster . may tektronix 555 has fuses soldered in for that reason. ?? ?I was lucky when the heat and aroma ?arose? when my S-47 was upside down in the sick bay. ? And it happens on 6 months old stuff too don again?? Now what about adding? micro smoke detectors in your HT exhaust ? ? From: [email protected] [mailto:[email protected]] On Behalf Of Rick W4XA ?? ¡¡¡¡¡¡ Disc ceramic caps shorting would seem rare but you never really know what a 60+ year old part will do! ? -- don??? va3drl |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
On Tue, Jul 16, 2024 at 01:09 PM, don Root wrote:
Yeah....No kidding!
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I even took it a step further and replaced the original HT-45 plate transformer (SEC voltage 6750VAC? center-tapped) with the Drake L-4PS transformer that requires a voltage doubling circuit (identical to the L-4/L-7 amps)
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There wasn't really anything wrong with the old plate transformer,? I just wanted to eliminate what I thought would be the next fault point:? The swinging choke in the HV line (and bleeder required minimum current necessary to make it 'swing')
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The original manufacturers of the old components that our old radios are using never expected these parts to still be in use 60-70 years later!?
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Even simple things like disc ceramic caps can (and do)? fail!
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In my HT-44, I had a screen bypass capacitor (C95 or 96 rated at 500V)? short to ground that caused? the 6DQ5 screen dropping resistor (R77) to quickly overheat..... with 250+ volts on it, that's roughly 35W!? I was pretty quick on the? switch but it was pretty obvious which resistor was R77!!!
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The HT44 sits on a desk and my wife came in the room to ask me something and standing right at the the thing If she hadn't noticed (the smell) right away, it would have surely caused some fireworks under the tube!
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Disc ceramic caps shorting would seem rare but you never really know what a 60+ year old part will do!
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
Comments is BLUE Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Tuesday, July 16, 2024 at 01:56:22 PM CDT, Rick W4XA <myr748@...> wrote:
On Tue, Jul 16, 2024 at 09:15 AM, Jim Whartenby wrote:
You're right.? The additional load due to the filament current is pretty much insignificant Not sure about this, see below:? ?
HV choke input power supplies? used tube type rectifiers in a full wave CT configuration and placed high voltage on the either the separate fil-transformer or integral filament winding in the main power transformer. Yes, I understand? ?
?Those filament transformer windings had to be designed to withstand very high operating voltages.? ?Yes ?
It appears that most (or all) of the (HT32/37)? main power transformers failed due to HV breakdown in teh filament winding.?
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I have failures here.? The separate? filament transformer in my Hallicrafters HT45 (pair of 866A rectifiers) faulted HV to filament.?
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In my HT32B, the filament winding in the main power transformer failed due to an HV short to the filament winding. What this indicates is that the filament winding has made contact with a wire in the HV winding layer just beneath it. Assuming a 1/2 volt per turn, the 5 volt winding will have 10 turns which is most likely in a single layer.? As long as only one connection was made to the HV by the filament winding, no harm done when going solid state.? But what mechanism is preventing a second internal short between the HV winding and the filament winding? ?
The problem is not heat in any integral HV filament winding, it's HV breakdown and it was so frequent in the
HT-32/37 series that they tried (it appears unsuccessfully) to "fix" it by redesigning the transformer.? This is the rub.? One end of the filament winding is connected to the HV winding at the rectifier socket.? The other filament winding goes to the other filament pin on the rectifier socket.? Lets say that the differences in wire thickness between filament winding and HV winding is 10X.? So the 5 volt winding over lays a 50 volt winding.? Is 50 volts enough to punch through the insulation of the two respective windings? ?
According to the tech service note on Walts site:
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If this indeed happened in 1959, then some of the HT37's and maybe all of the HT32A/B's should have gotten this updated transformer.
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My HT32B certainly would have,? but it still had the HV/FIL short. Then the failure mechanism is different from what is assumed.? On other words, it is not corona. ?
None of these failures would have been due to transformer over-heat unless the heat caused the "corona" condition.? I would think that's unlikely. Heat will cause minute movement of the windings as they expand and contract so this possibility should not be discounted.? All that matters is how many heat cycles have taken place over those 65 years since the HT was new. ?
It was an insulation breakdown (or the actual "Corona" condition)? that they tried to fix,? but it didn't fix it in my HT32B.
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The only sure way to fix it is to remove the high voltage from the filament winding. (Either by installing a separate filament transformer or solid state diodes ) Agreed, but either method eliminates the differential expansion between the filament and HV windings.? The filament winding is the prime mover with 10 watts of driving force.? We would have to calculate how much power is in the HV winding layer just below the filament winding but it is most likely much lower. ?
There is no way I would apply 700-900v DC to a filament winding in a 60-70 year old transformer now or in the case of the? HT-45,? Would I apply? 3000+ VDC to any old filament transformer. Well, if it is a separate transformer, the above mentioned movement does not exist between the two windings. ?
The smartest thing anyone can do in these old radios is to get the high voltage off the filament transformers or windings in main power transformers. This is interesting as an aside.? This is perhaps the only time I can recall where one is advocating the change to SS and ignoring the lower voltage drop of SS rectifiers vs the tube rectifier voltage drop.? This has been an on going debate on many reflectors.? <grin>? That said, I believe that you are right! ?
So changing to solid state diodes absolutely fixes the problem by eliminating the fault path. Well, we really don't know what the fault path is, we are only assuming that we do.? It will be interesting to see if the newest replacement transformers have the same problem down the line.? If any of us live that long! Regards, Jim ?
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
¿ªÔÆÌåÓýRick, Thanks for all that historical info it all makes sense, but to answer jims specific? question? in a little more detail the 5volt winding floats for a few cycles and then is forced to? HV by the rectifier conduction to the HV winding. When looking closely inside the transformer, it seems that there is a bit more to it. I was trying to write that to convince myself, but ?remove the tube rectifier ?and the 5V is no longer forced up to near B+. ???ohh, ?but do it before it gets too battered and has a T-T short too, and hits ?EOL ¡?? don?? ? From: [email protected] [mailto:[email protected]] On Behalf Of Rick W4XA
Sent: Tuesday, July 16, 2024 2:56 PM To: [email protected] Subject: Re: [HallicraftersRadios] HT-37 transformer failure due to rapid STBY-->OFF-->STBY ? On Tue, Jul 16, 2024 at 09:15 AM, Jim Whartenby wrote:
You're right.? The additional load due to the filament current is pretty much insignificant ? HV choke input power supplies? used tube type rectifiers in a full wave CT configuration and placed high voltage on the either the separate fil-transformer or integral filament winding in the main power transformer. ? ?Those filament transformer windings had to be designed to withstand very high operating voltages.? ? It appears that most (or all) of the (HT32/37)? main power transformers failed due to HV breakdown in teh filament winding.? ? I have failures here.? The separate? filament transformer in my Hallicrafters HT45 (pair of 866A rectifiers) faulted HV to filament.? ? In my HT32B, the filament winding in the main power transformer failed due to an HV short to the filament winding. ? The problem is not heat in any integral HV filament winding, it's HV breakdown and it was so frequent in the HT-32/37 series that they tried (it appears unsuccessfully) to "fix" it by redesigning the transformer.? ? According to the tech service note on Walts site: ? If this indeed happened in 1959, then some of the HT37's and maybe all of the HT32A/B's should have gotten this updated transformer. ? My HT32B certainly would have,? but it still had the HV/FIL short. ? None of these failures would have been due to transformer over-heat unless the heat caused the "corona" condition.? I would think that's unlikely. ? It was an insulation breakdown (or the actual "Corona" condition)? that they tried to fix,? but it didn't fix it in my HT32B. ? The only sure way to fix it is to remove the high voltage from the filament winding. (Either by installing a separate filament transformer or solid state diodes ) ? There is no way I would apply 700-900v DC to a filament winding in a 60-70 year old transformer now or in the case of the? HT-45,? Would I apply? 3000+ VDC to any old filament transformer. ? The smartest thing anyone can do in these old radios is to get the high voltage off the filament transformers or windings in main power transformers. ? So changing to solid state diodes absolutely fixes the problem by eliminating the fault path. ? ? -- 73/Rick -- don??? va3drl |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
On Tue, Jul 16, 2024 at 09:15 AM, Jim Whartenby wrote:
You're right.? The additional load due to the filament current is pretty much insignificant
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HV choke input power supplies? used tube type rectifiers in a full wave CT configuration and placed high voltage on the either the separate fil-transformer or integral filament winding in the main power transformer.
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?Those filament transformer windings had to be designed to withstand very high operating voltages.?
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It appears that most (or all) of the (HT32/37)? main power transformers failed due to HV breakdown in teh filament winding.?
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I have failures here.? The separate? filament transformer in my Hallicrafters HT45 (pair of 866A rectifiers) faulted HV to filament.?
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In my HT32B, the filament winding in the main power transformer failed due to an HV short to the filament winding.
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The problem is not heat in any integral HV filament winding, it's HV breakdown and it was so frequent in the
HT-32/37 series that they tried (it appears unsuccessfully) to "fix" it by redesigning the transformer.?
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According to the tech service note on Walts site:
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If this indeed happened in 1959, then some of the HT37's and maybe all of the HT32A/B's should have gotten this updated transformer.
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My HT32B certainly would have,? but it still had the HV/FIL short.
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None of these failures would have been due to transformer over-heat unless the heat caused the "corona" condition.? I would think that's unlikely.
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It was an insulation breakdown (or the actual "Corona" condition)? that they tried to fix,? but it didn't fix it in my HT32B.
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The only sure way to fix it is to remove the high voltage from the filament winding. (Either by installing a separate filament transformer or solid state diodes )
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There is no way I would apply 700-900v DC to a filament winding in a 60-70 year old transformer now or in the case of the? HT-45,? Would I apply? 3000+ VDC to any old filament transformer.
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The smartest thing anyone can do in these old radios is to get the high voltage off the filament transformers or windings in main power transformers.
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So changing to solid state diodes absolutely fixes the problem by eliminating the fault path.
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
¿ªÔÆÌåÓýAll ¡ has anyone physically looked at the off-on part of the Operation switch?. At first look one might expect it to be a wafer [ poor wafer] , but the schematic of the Ht-37 ?seems to show that it is not a wafer, but they do show and say under the ¡°AC on/off sw¡±? ¡°part of OS-??¡±. The parts list is no help at all¡..
which is not the same No. as the HT-32 I can send a snip showing just the OS area if it is any help? don -- don??? va3drl |
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
I don't understand how changing from a vacuum tube rectifier to a solid state rectifier has a positive affect on the power transformer's reliability.? The only difference that I see is that the load on the power transformer has been reduced by the 20 watts needed to heat the vacuum tube rectifier cathodes.? 5 volts X 2 amps X2. Does anyone know what the failure mechanism actually is?? Is it a failure of the insulation between windings?? Is it caused by heat induced mechanical movement of the winding or by excessive voltage causing the wire's enamel insulation to fail?? Or is it something else like the lead dress of the connecting solid and stranded wires?? Is the failure a dead short or a few ohms caused by a carbon tract? I assume that all of the failed power transformers were produced by the same vendor??? That the newly manufactured replacement transformers do not exhibit this HV secondary to rectifier filament failure?? Perhaps not enough time has passed to answer this last question. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Tuesday, July 16, 2024 at 09:49:14 AM CDT, hrd998cc via groups.io <hrd998cc@...> wrote:
This is a long thread, and I am very late to the party.?? Maybe this has already been discussed.? HT-37 transformer failures are common due to a failure/shorting between the rectifier filament winding and the HV winding.? Prevention is possible and simple by pulling the rectifier tube and replacing the appropriate diodes.? Russ KW6T
On Sunday, July 14, 2024 at 04:33:58 PM PDT, Rick W4XA <myr748@...> wrote:
Yup! I did say that! I was talking about Jim's mention of what a new transformer costs and I found it on Digikey! I apologize for not quoting what I was talking about! I have to say that if the transformer in my HT32B failed today, I would be ordering one from Digikey tomorrow! I wouldn't like spending $319 + Shipping/tax but if you think about it, that transformer probably cost around $35 new. $35 in 1963 would be almost $360 today! So it's a good deal if you have a transmitter in need of one! And you probably get one that isn't going to fail! https://www.in2013dollars.com/us/inflation/1963?amount=35 On Sun, Jul 14, 2024 at 02:19 PM, don Root wrote:
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
Yup! I did say that!
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I was talking about Jim's mention of what a new transformer costs and I found it on Digikey! I apologize for not quoting what I was talking about! I have to say that if the transformer in my HT32B failed today, I would be ordering one from Digikey tomorrow! I wouldn't like spending $319 + Shipping/tax but if you think about it, that transformer probably cost around $35 new. $35 in 1963 would be almost $360 today! So it's a good deal if you have a transmitter in need of one! And you probably get one that isn't going to fail! https://www.in2013dollars.com/us/inflation/1963?amount=35 On Sun, Jul 14, 2024 at 02:19 PM, don Root wrote:
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
¿ªÔÆÌåÓýRick, I began to think I would have to get on my knees¡ again and ask for forgiveness? then on my last gasp of searching I found: ¡°/g/HallicraftersRadios/message/30502 ?? At the end it says ¡° Just checked Digikey and the price is still $319 (plus shipping/tax)¡± I assumed it was an SSR that you were speaking of but on rereading you did not say what it is. ? Some good thoughts after the $,? ?but I have a few nitpicks to inject ??..later? don ? From: [email protected] [mailto:[email protected]] On Behalf Of Rick W4XA
Sent: Saturday, July 13, 2024 11:27 PM To: [email protected] Subject: Re: [HallicraftersRadios] HT-37 transformer failure due to rapid STBY-->OFF-->STBY ? On Sat, Jul 13, 2024 at 05:36 PM, don Root wrote: Well Rick, ?????back a little you mentioned 300+ bucks for one but maybe that is a dream? How did you determine that switching ON? is what wrecks the switch, not switching OFF ??, I worry about contact bouncing on the ON stroke and acring when it is turned off , especially under load.? I guess I¡¯m still wondering if it is a real toggle switch, or what.?? don ?
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Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY
If only once during the application of AC power is the issue then why use an SSR at all? The SSR forces the power transformer to see the same stress every time power is applied, the flux builds rapidly causing a counter EMF that is opposing the zero crossing voltage.? A mechanical switch on the other hand will make and break several times at random positions of the AC line voltage. My seven year old front loading clothes washer with a three phase motor and direct belt drive uses mechanical relays so perhaps SSRs are not always a good solution?? BTW, I have replaced the water pump twice, it seems to be the weakest link.? The coupling to the impeller breaks free so the motor spins but moves no water. Jim Logic: Method used to arrive at the wrong conclusion, with confidence.? Murphy
On Sunday, July 14, 2024 at 11:32:47 AM CDT, Rick W4XA <myr748@...> wrote:
I don't see where zero-crossing voltage is a problem since it only happens during application of AC power. There is no collapsing flux since it hasn't been established. The SSR's during turn off, don't "disconnect" (if that's the right word) until at "zero" current. From the Opto22 spec sheet: And actually, there is a "chance" every time one turns any piece of gear off, of having the contacts open at the "right" (or wrong) time(or somewhere in between) . I have "pulled the plug" on many devices while they were powered and sometimes there's a spark and a "snap" and/or see a spark and sometimes there is not. Turning the radio off then right back on is of course another issue regardless of how the circuit is interrupted either by a switch, relay contact or Triac. I cannot think of any reason why one would do that intentionally. And in the case of the original question I am afraid I have diverged from it by even mentioning the use of SSR's to reduce switch failures (as is the mention of step-start systems etc) REF: HT-37 transformer failure due to rapid STBY-->OFF-->STBYCan someone please indicate the page in the HT-37 manual where it says NOT to this? While I still cannot think of a reason why anyone would do this, I only found the "CAUTION" text I excerpted and posted earlier. (that is, to pause in STBY before turning it off) After printing out a pretty good copy of the HT37 schematic and taping it all together so as to see what's going on, (OPERATION SW is in the OFF position) .... It appears that the transformer remains powered and all voltages are present until selecting OFF. There are 3 wafers that control bias switching, and other low level "stuff" The only thing I can see that could be a problem is if one was doing RTTY , transmitting at full power, and then went from MOX directly to OFF, there might a problem with MAX AC current in. But that's just a guess . Again, I don't see how it would be a problem if the transmitter wasn't transmitting (or keyed) Again, the original "question" concerned OFF-ON-OFF rapidly. No reason to do it, so don't! Sorry for the long answer! 73/Rick On Sat, Jul 13, 2024 at 11:37 PM, Jim Whartenby wrote:
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Re: HT-44 VOX issue - Final Solution!
Great Pics On Sun, Jul 14, 2024 at 2:28?PM Floyd - K8AC via <floydsense=[email protected]> wrote: Here's a scope trace of sending three dits at around 25 wpm. Note the shortened length of the first dit and the lower output level compared to the second and third dits. |
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Re: HT-44 VOX issue - Final Solution!
Here's a scope trace of sending three dits at around 25 wpm. Note the shortened length of the first dit and the lower output level compared to the second and third dits.
Here's how three dits look after Winkeyer USB is setup to extend the first dit or dah by 30 milliseconds. While the first dit is now of the proper length, the power level is still lower than that of the second and third dits. The parameter used to lengthen the first code element by the Winkeyer is called "1stExt" for first extension. It works for hand sent code or for messages sent by the PC to the Winkeyer. Another oddity - there's always a very short noise burst about 25 ms. prior to the start of a dit or dah. Not noticeable on the receiver. Looking close at the envelope for a dit, the rise and fall times could be a bit longer, but the shapes are pretty good. Here you can see a variation of several percent in the output power level over the duration of the dit. |
Rick W7IMM
Paul Christensen
don Root
Jim Whartenby
Dave Jordan
Floyd - K8AC