JCM2000 output transformer primary winding resistance.

Sprywatt

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G'day.

I've bought a new transformer from Heyboer to upgrade my JCM2000DSL 100W.
I checked the existing DC resistance of the stock Dagnall and compared them to new Heyboer (100W).
The Heyboer is approximately 60 Ohms from end to end (30ish wrt center tap). The Dagnall is half that, 30 (16 wrt center tap).
This would result in the DC current being halved with the new transformer? It's been a while since my transformer topic, and that this doesn't include AC impedance (guitar signal from anodes in push/pull).

Anyway, just after some guidance/assurance so I don't let smoke out.

Cheers.
 

Pete Farrington

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Here’s the Hammond replacement, 30ohm primary resistance https://www.hammfg.com/files/parts/pdf/1750X.pdf
Perhaps the Heyboer is an upgrade, eg higher primary inductance due to more turns hence more resistance.
Peak current will be maybe 700mA per side, so there won’t be a ha’penny’s worth of difference between the effect on anode voltage of 16 or 30ohm resistance.
 
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william vogel

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I don’t think the DCR is going to have an adverse effect on the performance but I’m also surprised that it’s nearly double what is typical of a 100 watt Marshall output transformer. Surprising! That DCR is comparable to a 50 watt output transformer. Hmmm!
 

Sprywatt

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Bit of a late update.

I installed the OT about a fortnight ago and wow. My brother (who I am in a band with) has a stock dsl100 like mine. With the choke and new transformer in and on the same settings as one another, I can't believe the difference. Sounds like a completely different amp...for the better! Cuts through like a knife!
 

Tatzmann

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Might install a choke into the other DSL too
to see what made the biggest difference?!

Have a 2000 DSL100 too and would consider a choke if it considerably benefits from it.
 

mickeydg5

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Bit of a late update.

I installed the OT about a fortnight ago and wow. My brother (who I am in a band with) has a stock dsl100 like mine. With the choke and new transformer in and on the same settings as one another, I can't believe the difference. Sounds like a completely different amp...for the better! Cuts through like a knife!
Is the Heyboer a HTS-11517?
If so, it is a 2200 impedance most likely made with a bit more windings but smaller than average diameter wire to achieve 100W rating.
It will drop more voltage while providing a bit less current at frequency.
 

Sprywatt

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Might install a choke into the other DSL too
to see what made the biggest difference?!

Have a 2000 DSL100 too and would consider a choke if it considerably benefits from it.
Yep! That is the plan. I managed to grab a hold of one of the last few Classictone chokes recommended in the joey mod thread. So old mate will have to settle for a Hammond or something. Might try the Mercury o/t for him too.
 

Sprywatt

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Is the Heyboer a HTS-11517?
If so, it is a 2200 impedance most likely made with a bit more windings but smaller than average diameter wire to achieve 100W rating.
It will drop more voltage while providing a bit less current at frequency.
Invoice says HTS-9707. I'll double check the sticker on the unit. All I remember it saying was that it's a JCM2000 TSL.
 

Sprywatt

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One more thing. I took some measurements of both new and old transformers at work using our LCR meter. I thought I'd use the square root of L1/L2 method to determine the impedance.
The unit was a bench top so it had a few extra settings rather than a hand held...but the numbers didn't end making much sense (kinda low).

I got the following for the new one's primary:
@100 Hz = 18.78 H
@120 Hz = 13.3 H
@10kHz = -743mH
@25kHz = -115mH

Secondary: (from 16Ohm to Common) I assumed common is the bottom of the winding and 16 (being the highest resistance) would be the top? 8Ohm half way 4)hm 1/4 etc etc.
@100 Hz = 385m H
@120 Hz = 166mH
@10kHz = -6.6mH
@25kHz = -933mH

I wasn't sure if the frequency sweep was necessary since (if i remember correctly) Inductors are kind of like open circuits at high frequencies. So I picked the values at 100 Hz and used those giving me: square root of 18.78H / 385mH = ~7Ohms? From my understanding in my amp book, this value should be in the kilo ohm region?

The old transformer I did the same and got the following

Old one's primary:
@100 Hz = 1.9 H
@120 Hz = ~1.95 H
@10kHz = -388mH
@25kHz = -50mH

Secondary: (from 16Ohm to Common) I assumed common is the bottom of the winding and 16 (being the highest resistance) would be the top? 8Ohm half way 4)hm 1/4 etc etc.
@100 Hz = 66.8mH
@120 Hz = 66.8mH
@10kHz = -15mH
@25kHz = -1.9mH

Using the same formula as the first one, I got an even smaller value (@100Hz) of 168mOhms?

I know I've gone wrong somewhere, if anyone can shed some light on where, that'd be great.

And if anyone has any books, resources on in depth transformer design, that would be awesome. I'm thinking of these as my old resources don't really deep dive into everything.
https://www.routledge.com/Transform...oulin-Feghali-Shah-Ahuja/p/book/9781032339528

https://www.booktopia.com.au/handbo...ns-william-m-flanagan/book/9780070212916.html

Thanks!
 

Pete Farrington

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I’ve not tried it, but I’ve read that if the secondary is loaded by a resistor whose value is the intended load impedance, an LCR meter can measure the resulting primary impedance.
That method also incorporates the effect of secondary (and less significantly, primary) winding resistance.
 

william vogel

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I wouldn’t disagree that there should be a way to use a LCR to calculate it but using a voltage is sure fire. The most accurate way to do it with a voltage is to use a frequency that’s known to be within it’s frequency spectrum. On a guitar output transformer 120hz would be better than 60hz but sometimes we don’t have that available. Merren told me this about measuring old transformers that were made with sh1t steel. He said the old steel is going to give lower numbers (slightly) on lower frequency because it’s not efficient enough in that range.
 

Sprywatt

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If you want to find the turns ratio. Apply a voltage ( 100 volts AC) to the full primary and measure the secondary voltage output.
I did forget to mention that. I've bought a Variac but not used it yet. Is using a modified kettle chord and applying it to the primary going to be okay? I've seen other people use another intermediary transformer, use a lower amperage fuse. Any tips would be great, thanks.
 

Pete Farrington

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Merren told me this
Over on the old vintageamps forum, he was emphatic about using a high excitation voltage when testing winding ratios to deal with magnetisation losses.
However, testing this using a variety of OTs, I didn’t see a difference in using the (low impedance) output of my sig gen directly at maybe 2Vpk, compared to using a solid state power amp to boost it to about 50Vpk.

I mentioned incorporating the secondary resistance, as with vintage OTs / clones especially, it may be significant.
eg 1ohm secondary resistance will get ratioed up to perhaps several hundred ohms at the primary. That needs to be added to the calculated primary impedance.
Or alternatively add the secondary resistance to the nominal secondary load before multiplying by the impedance ratio.
 
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william vogel

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I did forget to mention that. I've bought a Variac but not used it yet. Is using a modified kettle chord and applying it to the primary going to be okay? I've seen other people use another intermediary transformer, use a lower amperage fuse. Any tips would be great, thanks.
I just hook my variac directly to the full primary. I have a plug I cut off an extension cord and use the hot and neutral. I turn up the variac slowly and turn down slowly. I also have meters on both the primary and secondary to note the 100 volt primary and the secondary voltage. I think as long as it’s a known good transformer that’s being checked your okay without isolation. I do it quite often.
 

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