audio-talk

Just spent four hours unstacking one of my 5K a-a push-pull output transformers. I want to try and make a 5K SE OPT out of it: something that will perform with one of those 45s Melanie told me to “put on a bit of wood or summat,” but I’m not sure whether it’s possible to do so.
I know the bit about having all the Es facing the same way and butting all the Is up with a bit of paper between to make an air gap, but I just know it’s going to be one of those ‘well you can’t just take one thing then turn it into another” scenarios.

The question I have, is:
“Do you think that’s wise ?”

I probably should have asked before I took the bloody thing to bits, but I’ve done it now.

Whoo !
There's at least one person on here who can advise you, I'm sure

We used to leave intact and connect as a parafeed.
But now you’ve got the lams de-constructed it’s a question of experimenting with the gap.

Make up a PI filter start with but gap increase gap a thin piece of paper and add layers one at a time. When you get best regulation at 36 mA dc passing through: that’s youre gap for youre scenario.

Calculate the inductance with ripple in to ripple out, knowing capacitance, to solve inductance. Check -3db frequency, of the low pass filter; decide if it’s low enough.

Remember SE is a compromise at LF. Don’t expect miracles, core size is bigger for SE than push pull, but don’t let that put you off. Try it.

The ratio remains correct using full P to P primary.

Looks like I'm gonna have some fun with this.
Transformer number 2 is about to start being unstacked.
I'll have plenty more questions later on: no doubt about that.


Stack is 1 and 1/2in thick.
Core window is 2in high x 1and 5/16 wide as is the tongue of the E sections when stacked.

4 hours for the first one. 3 hours for this one.
I’m getting better. This photo shows the tools I used to get it apart.

A good swirl of Optrex followed by a stiff drink is in order now.

Don't get those mixed up !

Looks ideal size for 1.6 watts 36 mA. No harm playing with it.

If you have too small a gap the distortion is the nastiest sound I’ve heard from a valve amp, and a complete embarrassment if you take some untried transformers you’d brought to a meeting with Vry, Morgan Jones and Mike Lefevre. I’d bought them at considerable cost, but not tried until that day. Not enough gap, improve the gap, not enough inductance. Sound I couldn’t describe, they were so bad distortion I’ve never experienced so nasty in any other way.

You’re playing with fire, it takes years to get a new skill on youre own and can send you mad!

The best resource which is readily available and freely provided these days is Turner Audios blogs on transformer winding interpretations of all the relevant sections of RDH4. You won’t find such an honest and thorough interpretation and open free sharing of audio transformer winding.

Here’s an example http://www.turneraudio.com.au/output-tr ... alc-1.html

Someone needs to preserve these pages you never know when the Authors not around any more. I couldn’t glean the great tomb of knowledge in RDH4 that Turner has gleaned and presented to us freely. It’s a remnant of the informative guides from an era before advertising revenue dictates results of internet searches.

Thanks Paul for that link, there’s loads of stuff, that as you say, would be almost impossible for anyone to put together as coherently these days.

Paul Barker wrote: ↑Thu May 13, 2021 6:25 am Looks ideal size for 1.6 watts 36 mA. No harm playing with it….

….You’re playing with fire, it takes years to get a new skill on youre own and can send you mad!

At least it has a chance of working as it’s a good size. The way I look at it, is that these transformers (now in bits) don’t owe me anything. They are old and TBH would never have got used again. They’ve also given me an opportunity to examine how transformers are put together.
My attitude is, if they work that’s fine, if they don’t then it’s a learning opportunity and I haven’t lost anything except a few hours spent dismantling them. I have no emotion invested in them, but it’s a fantastic opportunity to learn something and to blow the dust off my ‘scope and signal generator.

Yes to all that. Worst case scenario wind them as chokes. Nothing lost.

Oo interesting.

The reassembly is underway on one of the transformers. Lams have been stacked on a dead flat surface ie. a mirror, so that the mating surfaces for the gap will be as uniform as humanly possible.

‘E’ Lams have been varnished with 50/50 mix of yacht varnish and white sprit, so that it was sufficiently diluted to sink easily down, by capillary action, between the lams when applied.
Once the varnish had soaked down through the structure, the lams were clamped up, squeezing the excess varnish back out again.
The ‘I’s were treated the same then clamped up tight making sure that the stack of lams was an interference fit between the two flanges at the top of the core former. I would have hated to have done the ‘I’s only to have found that the stack was too wide to fit on the top of the former.
The mirror has kept everything dead flat and absolutely square. It’ll be left for a couple of days to cure, whilst I rebuild the other TX.
Whilst the other TX is curing, I can start testing the first one. That’s the plan anyway.

Good job. Sowter presentation of their EI transformers has the quality of finish which someone whose never assembled a transformer would not know or notice. A generational family business makes it no drama; it looks good as if it was a simple job. But there are many elements of total care and concentration as which ever generation carries another transformer paying care about quality, naturally but unseen and mostly un-noticed.

That thread seems to run in you’re family.

Paul’s mention of parafeed got me thinking. You could do a test with no intentional air gap, which I think would give you the best LF response. And use an active load (CCS) with cap coupling to the OPT.

This is what Nick suggested to me as a way to get the best out of my interstage transformers (albeit push-pull in my case)

Also I have good memories of hearing deco-doctors parafeed amp (at one the Owstons I think)