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Dynaco Stereo 35 replacement output transformers

nerdorama said:
Just came across this ad while searching for something else. Anyone ever heard of them?
https://reverb.com/item/65255813-pacific-transformer-dynaco-st35-output-transformer-2023
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$173 each? :eek::eek::eek::eek::eek:

Spec sheet is here: https://cdn.shopify.com/s/files/1/0519/5956/2405/files/PAM-OT-35-73R_Spec_Sheet.pdf?v=1665759399

Looks like they are 7/8" wider (4" vs. 3.125") compared to the ones from DynakitParts.com so not sure if they would fit.

This (attached) seems to be Hafler's patent for his then-unique transformer design. It's enough to make my head spin. You wind this in this direction then wind this over that and then go the other direction and add another winding this direction and on and on and on. Yikes. I wonder how many of the manufacturers selling replacements today are actually following the process and not just providing a "similar' or "suitable" replacement.
 

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nerdorama said:
Some years ago I did as you suggest and mounted an aluminum plate with 4 sockets and hardwired my circuit. It was just an experiment which worked but not completely successful.
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Yes, that's the idea. Which tubes did you use? I'm guessing one might be 6C4. What problems did you have? I would probably start a project like this with a pair of EF86 driving a 6SN7 (three tubes). There are many options once you move to a panel instead of a PCB.

Jack
 
I was trying a plate to plate feedback scheme using some 7 pin pentodes as a long tail pair. It worked but had a lot of hiss as I remember. Also made a plate with 9 pin sockets for a similar trial. I think it may have worked using EL84 as the drivers. Probably wouldn't have the noise issue.
 
The out of phase winding direction makes me wonder if there was any inspiration from Neutrodyne radios of the late 1920s. Those had a couple turns going the wrong way on the RF coupling transformers to reduce the tendency to oscillate.
 
That is pretty much how it's wound. The ultralinear taps must be included off course. I want to comment on the "reverse" winding. It isn't wound in reverse, the spool turns the same direction. It is merely started from the opposite edge, giving it the appearance of being wound backwards. I can see no point in "bucking" the magnetic field created.
 
stanko said:
the "reverse" winding.
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The Hafler transformer patent is attached for anyone interested. I don't know what he means by "identical sense of rotation" and "opposite sense" in column 4, lines 22 and 24. There also is a drawing referring to rotational sense. It's confusing to me. Perhaps it has something to do with the right hand rule.

Also attached is the ultralinear patent.

These are the first two patents by Hafler.

I have a strong suspicion that many sellers offering "replacement" ST-35 transformers are not following this patented (formerly) process. If not, that would mean that they are not the same at all even if they may work.
 

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Yes, they call it "sense of rotation", it looks like it's backwards. Take a toilet paper roll, wrap some string around it, starting at your finger. Then start at the far end, wrapping the same way, but towards your finger. It will look like the windings are backwards from each other even though you wound in the same direction.
 
I'll take your word for it, but when I wind a fishing reel, I go back and forth from one end to the other with the line and never consider anything backwards. Must be an engineering notation/language thing. :dunno:
 
JustMe2023 said:
I'll take your word for it, but when I wind a fishing reel, I go back and forth from one end to the other with the line and never consider anything backwards. Must be an engineering notation/language thing. :dunno:
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Correct, and that's how a transformer is wound.
 
Like this?

upload_2023-4-4_18-33-39.png

The picture does make it look "backwards" so to speak even though the direction of the widing rotation is the same.
 
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Yes, it looks like it's wound backwards but isn't. The rotation is the same.
 
These transformer discussions with Hafler in the year 2000 are an interesting read, combined with his patents that I posted earlier.

The DynakitParts transformers can't be exact copies since they have 4 ohm taps instead of 16. I wonder if they perform any differently because of it. On both of my tube amps, I find the 4 ohm taps useless even though my speakers do present a 4 ohm load across a large portion of their range. I think I would have left the transformer alone with the 16 and 8 ohm taps but moved the NFB to the 8 ohm tap. YMMV
 

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JustMe2023 said:
These transformer discussions with Hafler in the year 2000 are an interesting read, combined with his patents that I posted earlier.

The DynakitParts transformers can't be exact copies since they have 4 ohm taps instead of 16. I wonder if they perform any differently because of it. On both of my tube amps, I find the 4 ohm taps useless even though my speakers do present a 4 ohm load across a large portion of their range. I think I would have left the transformer alone with the 16 and 8 ohm taps but moved the NFB to the 8 ohm tap. YMMV
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I agree.
 
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