Halden ?, Jim too

One part that doesn't make sense to me is the one about the 5V windings being "connected" to the B++ windings.? They're only connected when the insulation fails and the arc is active, and only one of them is known to do that.? ?

Maybe ?I’m ?guilty of using insufficient wording ??"connected" to the B++ windings. ?I meant ?"connected ?thru the 5R4” to the very HV windings.

?I still cant think of an accurate simple expression. ?Is that any help?

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The other part that doesn't make sense to me is "When one 5 volt heater winding is at +800 RMS".? RMS is a way of quantifying an AC signal over time and is not an instantaneous value.

thats probably me too. I agree that it may be easier to use instantaneous values. ??As I see it, there a +800 RMS"

for one half cycle and a -800 RMS" half cycle ?also ?each half cycle of the HV takes its turn at grabbing the filament winding and sending very pos or very neg, with the peaks being ?800*√2? which is 1131.3708499 according to google.

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My hi-pot testing uses DC.

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I didn't measure the 800 Vrms directly because I don't want such high voltages around when I'm working alone.? So I used the secondary of another transformer to apply 20 Vrms to the primary and then measured the voltages at various taps on the secondary.? All measurements used a Keithley 2000 DMM, so I'm confident that the RMS values are correct.? Then, I assumed linearity and multiplied my result by 5.ok? Now that I wrote this down, I see it was an error - I was trying to think too fast!??? I should have multiplied by 5.8.? I would use 6 assuming a 120 volt primary but it may well be rated at 115, but we don’t know, do we? ??So, where I wrote 800 in this morning's post, it should be 919.? 1130 should be 1300, 1100 should be 1260, 2230 should be 2560, and I should probably turn my Bertan up to 2600 V next time. ?

you effectively had the turns ratio? measured, ??

I was only wondering if Hammond ?had the same turns ratio, they said ?120 /880volts ?or a ?1:8 ?ratio

I don’t know enough about Hi-pot, especially DC and on used transformers, so…

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If the 5V secondaries are likely to be 10 turns, then both 5V secondaries and the 6.3 V secondary are likely to be on the outer layer of windings and accessible after digging through a few layers of crisp paper and varnish.?

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Maybe I could find the arcing spot and add insulation to repair it.? I'm now tempted to open up the transformer and look.

Good , It might be creepage around the very ends, so test before you get the scalpel out , ?oh ?I’m late hope the tipoes fix themselves on the way.

don

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Jim ,

Re ?“It was not reported that a short circuit involved the common ground tap so I am not sure that this is of concern.?“

maybe Halden understands you, but I don’t.?? I cant see any “short circuit involved the common ground tap “ ??but he did mention the HV CT ground in passing. As I read it ?????He did not seem to be concerned IMO.

However, It is important to state where grounding is, otherwise voltages might float very high wrt gnd, and it is tough to convey voltages .

Having that ground means that one terminal cant get above 800 or whatever that really is, so stresses to ground are known, all assuming the core is grounded too and grounding really means “chassied” at near local mother earth.? I’m sure you know all this, but maybe glossed over the wording.. sorry if that’s wrong.

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I think it was not necessary to speak of? the other windings as the reported failures are from the HV and the 5V [5R4] wdg where ever it is, but when you look at obvious paths to breakdown from the HV, one expects that ??HV wdg to 5V [5R4] wdg ?has a weak insulation path by design, or perhaps by manufacturing QC and this. ??disconnecting? that 5 volt winding? will remove that high stress? before the transformer fails and after.

Hi Halden

Your posting just poped up when there is no load on GIO.

I also have contorted my head trying to get at the crux of this failure, and the reasoning behind it using other wording. Your reasoning and wording seems very good to me, and matches what I read from Jim’s writings. ???But

Jim is using peak voltage so gets over 2kv ?rather than 1600 [800+800] or what I used 1760 ?from Hammond’s ?replacement, I think Hi-pot is in rms values.

When it gets to accuracy, there are a few questions/comments:

My 1720 rms values don’t include any fudging for transformer drop or tube drop.

I wonder what the primary voltage and operating mode ?conditions were when you got 800 VAC; the reason being halli did not state a single rated voltage input such as 120 vac, but instead presented a range of useable voltages 105 to 125, and I cant see any place where the AC input is stated in the voltage chart , nor could I see the operating mode etc, ?

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Jim ???re?? ?The 5 volt windings see twice this for a total difference of 2.488 kV.

Make sense?? ?????????Yaaaaa! ???But we usually speak of rms in dealing with insulation, but the peaks are still there too.

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Jim, I looked all over but cant find much on real construction for tube rectifier transformers.?? R e your construction—sounds good to me. If I was going to build one, I’d try that.

That makes sense. But it will be twice that between the HV ends 880 + 880 =1760 rms ??and a real problem due to the 5v location.

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Jim, re “ …. This would put perhaps more then a KV difference ?between one 5 volt winding and the second HV winding sitting just below it ?

I wonder where you get the voltages from . ?we can see on the tube voltage chart 760 VDC on the filament ?but nothing about the plates and nothing about the transformer voltage that I can see. ??And I could not understand some reported voltages and I can’t see some in the halli-manual ?but I finally found this:

Presumably 880 is a no load voltage so it will run slightly lower depending on operating mode etc

After much head scratching it seems that 880 VAC should boil down to something like 760 VDC for a choke loaded ?rectifier so now I “see” 1760 rms volts across the HV terminals and that would be the prime stressor of that insulation, but under your construction idea, which must be close to the actual the 1760 will only take place between the 5V wdg and the nearby HV wdg , as you implied I think. So I am of the same thinking other than your? “ more then a KV”

it could be at the end of a layer and the wdg to wdg insulation ?is not wide enough, and there is a creepage path ?around the end

and perhaps corona.? Of course the 1760 could just breakdown? the insulation, as most people know the very ends have higher field intensity

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Rick? ???

?edited /fractured a bit ???????????

Re ??Back to the original "Re: HT-37 transformer failure due to rapid STBY-->OFF-->STBY" subject of this thread,

I think topics get started before they get properly thought out; this one is not bad but perhaps too specific and not quite what was intended

?I forgot all about? Halden’s?? actual title???? …”transformer failure ?due to rapid? ?STBY-->OFF-->STBY” ?I think that nobody read the word phrase that Halden actually wrote in the title. ?It seems to me? the general? switching? involving ?????the “STBY” position has been grouped into one PROBLEM AREA, so the real failure condition has been diluted into muddy waters, ??EXCEPT THAT? ?THE “STBY” SWITCHING IS ALWAYS INVOLVED

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I would like to remind us all that Halden ??later re-worded? his concern? in??? /g/HallicraftersRadios/message/30429 ?saying partly..

“I still wish to understand how turning the transmitter off without a pause in STBY, or turning it fully off and immediately on again, can cause a voltage spike between these windings that’s substantially in excess of what occurs during operation, and could cause an arc between windings and thus deteriorate the insulation at the arc site.?“…. Etc? ?

There are still two situations in that question:? turning “to OFF” and turning “away from OFF”

Personally, I think its worth considering any/all the situations. But it is hard to sort them out, as we have seen

?there's isn't any mention of doing this.? Agree ?

The only "Caution" is to pause in STBY before turning it off ???????and they don't say why.? ?

Agreed on both points long ago ,a n d? …. they don’t say why because they have red faces, and can’t easily fix the problem- only a US ?senate inquiry would extract the true culprit.

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As to some other comments it seems that the switching caution/problems and ?transformer failures were all part of the new stuff in 1959 and not related to age, but things do deteriorate years later also ?

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Rick and jim

?Re You are most likely correct, if the power transformer is still good after some 60 odd years, it may not fail, at least in that manner.??

How many ways do you think there are to smoke the HT-37 transformer? Just one? ?

I am a professional knob-speed-twisting-tester and can prove you wrong--- on your rig.

The original owners read the bible before plugging it in,? but then some others don’t, just plug’er in, turn the knobs and find out what happens.. that is what they are there for!!?

…. CW via smoke signals!