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Hand wind a push-pull audio output transformer?  

 
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator

Hi all,

Does anyone what it would take to hand wind a push-pull output speaker? (or two) - I have a nice, but simple enough, circuit diagram for a basic push-pull valve audio amplifier, but the transformers are way too pricey for me, and more so since I really rather fancied building a stereo version, or two monoblocks.

The amp would have only been quite modest, at around 3W-5W output, using ECL82, or similar triode/pentode valves.

More than anything, I was looking at a project that would let me test myself again, before getting into something more important.

If it ain't fixed, don't break it!............

Quote
Posted : 27/11/2019 9:54 pm
PYE625
(@pye625)
Famed V-Ratter Registered

Hi Marion,  guess you mean a transformer wind rather than in the actual speaker coil itself?

Unfortunately, it is the output transformer quality that is crucial to sound fidelity and of course stability within the amplifier. As a consequence, a really good transformer is not easy to wind especially if you need an identical pair for stereo. This is why they can be rather expensive.

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Posted : 27/11/2019 10:34 pm
Cathovisor
(@cathovisor)
Famed V-Ratter Registered

Hi Marion,

short of keeping an eye on eBay for pairs of transformers from scrapped German stereo radios (it does happen) there's always this:

http://www.radiofil.com/transfo-de-sortie-r-tu-101-l-unite,p451.html

Sadly, only available to Radiofil subscribers.

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Posted : 27/11/2019 11:04 pm
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator

@pye625

Hi Andrew,

Err, yes, that's what I meant, but my brain likes to fart and fall back on its arse from time to time. . . . . It was meant to read "speaker output transformer"

I have a few old single ended transformers, and was musing over rewinding them in a push-pull configuration, if indeed it could be done, but I had no illusions of a simple task, but from what you're saying there, it's not really going to fly - and I guess that any usable reclaimed transformers are in big demand for just this purpose.

I looked on eBay, and when numbers like £115 for a pair started coming up, I pretty soon concluded that it's not going to be affordable for me, not for quite a while anyway.

I don't mind presenting the circuit diagram, if anyone else fancies building it? It's originally out of my granddad's book of odds and sods, where he would scratch out things like this. It was labelled as "General purpose push-pull amp for Dynatron TV set". Whether that meant he was planning to improve on what was already in a Dynatron set he was working on, or if he'd seen it in a set somewhere and reverse engineered it as a future project, I couldn't really say, but he did have a bit of a collection of useful circuits for all sorts of applications.

It was designed around ECL82, but I was thinking of tinkering with PCL82, since these are a magnitude cheaper to buy. It had only a volume control in this diagram, so could have been interesting to add tone controls, and maybe some switchable inputs.

If it ain't fixed, don't break it!............

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Posted : 27/11/2019 11:29 pm
PYE625
(@pye625)
Famed V-Ratter Registered

It can be rewarding sometimes on ebay, for example, old radio/stereogram chassis etc can appear from time to time. Some investigation re. model numbers may be needed to see if push-pull transformers are used though.  ECL82/3/6 types would be most useful of course, but even 6v6 types could be used without problem.

(For example, a search "push-pull ecl" on ebay revealed some reasonable results just now.)

 

To understand the black art of electronics is to understand witchcraft.
Andrew.

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Posted : 28/11/2019 9:47 pm
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator

@cathovisor

Hi Mike,

That's not a bad idea, though a quick look tonight hasn't revealed much, but then for some reason I can't find a pair of glasses good enough to see text that well - for example, I read your comment as "Germanium" stereo radios. Definitely still having problems in that quarter, more over, I've had a full raft of meds today, so not really "Top Santé" tonight.

I'm not done yet!

If it ain't fixed, don't break it!............

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Posted : 28/11/2019 10:32 pm
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator

@pye625

Hi Andrew,

That's also a good suggestion, though it'll be another night now, I've been over there, and my next stop is bed, after I finish here, but I'll be trying both yours and Mike's suggestions.

Mind you, what counts as reasonable, might well still be out of reach for me right now.

Not planning to try this, but curiosity makes me ask, can two SE transformers be wired together to obtain a push-pull output? - I can imagine a million and one things that say "no". . . .

If it ain't fixed, don't break it!............

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Posted : 28/11/2019 10:39 pm
Red_to_Black
(@red_to_black)
Noble V-Ratter Registered

Nice to see you back Marion 👍 

You have been missed 😊 

"This is my multimeter. There are many others like it, but this one is mine. My multimeter is my best friend. It is my life. I must master it as I must master my life. Without me, my multimeter is useless. Without my multimeter, I am useless."

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Posted : 28/11/2019 10:39 pm
Katie Bush
(@katie-bush)
Famed V-Ratter Moderator

@red_to_black

Hi R2B,

Thanks, and it's nice to be here again ✔, though I'm still hitting a few problems. . .  🤦

If it ain't fixed, don't break it!............

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Posted : 28/11/2019 10:48 pm
Cathovisor
(@cathovisor)
Famed V-Ratter Registered
Posted by: @pye625

It can be rewarding sometimes on ebay, for example, old radio/stereogram chassis etc can appear from time to time. Some investigation re. model numbers may be needed to see if push-pull transformers are used though.

Good call. I think the Bush SRG86 has push-pull output and is stereo too.

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Posted : 28/11/2019 11:17 pm
turretslug
(@turretslug)
Reputable V-Ratter Registered

Some Eddystone receivers use a small push-pull output transformer with 2x EL91 bottles for a few watts of what might be described as good comms quality or OK listening quality, but I don't suppose they come up for sale terribly often- the receiver circuits might provide some inspiration, though (ISTR the various model 680 versions and their model 730 professionalised incarnations). Reading between the lines, I think that Eddystone had painted themselves into a bit of a die-cast corner and wished to claim reasonable output power, 5W or so, without making either mains or output transformers too big and making use of mains transformer and castings stocked in depth for other simpler models, as opposed to any aspiration towards hi-fi!

I found this outfit whilst looking for HT-type transformers generally- usual disclaimer;

http://primarywindings.com/product-category/outputtransformers/

including a teensy 4W push-pull transformer that's not exactly hi-fi in spec. but interesting in concept. I have a carton of NOS QQV02-6 that are looking for employment- it struck me that they aren't light-years from the ELL80 in general concept (aside from a commoned screen-grid, ruling out "ultra-linear" operation). They were intended as small high-VHF/low-UHF push-pull PAs, so would obviously need sensible layout and stopper resistor precautions to stop them mis-behaving as AF amps. Half-tempted to look for a small P-P output transformer, too.

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Posted : 29/11/2019 12:18 am
Alastair
(@alastair)
Reputable V-Ratter Registered

Hi Marion,

Look up Dissident Audio, a French website mostly in English, and download his output transformer design assistant program. Its in vers 3.22 now, I used it some years ago, at 1.5 Works out well.

When you input A-A impedance and output impedance It'll tell you how many turns per layer, how many layers per coil how many coils can be used on that size stamping of your choice, plus thickness of insulation and expected inductance and capacitance when finished.

Takes all that boring maths out of the job.

It does both SE and P-P. Frames, enamelled copper and stampings can be got from almost any transformer winders but you have to be specific as to exactly what you want.

 

 

 

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Posted : 13/02/2020 11:06 pm
Alastair
(@alastair)
Reputable V-Ratter Registered
Posted by: @katie-bush

@pye625

Hi Andrew,

Not planning to try this, but curiosity makes me ask, can two SE transformers be wired together to obtain a push-pull output? - I can imagine a million and one things that say "no". . . .

Yes they can, and can be done in two ways. Just wiring them up series/parallel arrangement or by removing the 'I' stamping and clamping both together making a single trans out of the two, I did this 30 odd years ago using two PCL82 trans you know, the red coil wired ones. Every set had one that used the ECL82.

I guess this could also be done with power-transformers as the main issues with those used in SE was core saturation, but two made as one that'll be cancelled, and I guess a lowish say, 10W P-P of acceptable quality could be made this way.

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Posted : 13/02/2020 11:14 pm
Nuvistor
(@nuvistor)
Famed V-Ratter Registered

There is a good write up of a Thorn radiogram with switching for push pull in mono and single ended in stereo using separate output transformers. I saw the circuit first in a USA mag, think it was RCA but could be wrong. Thorn had close connections with RCA and other USA companies.

page 500

https://www.americanradiohistory.com/UK/Radio-Constructor/60s/RC-1966-03.pdf

A good read if nothing else.

Frank

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Posted : 14/02/2020 10:47 am
Cathovisor
(@cathovisor)
Famed V-Ratter Registered

@nuvistor

That was done on some of the the high-end SABA radios in the early 1960s.

 

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Posted : 14/02/2020 11:19 am