Restacking An Output Transformer.

[Wolfgang]

Parafeed with CCS is probably the best way because a very high quality inductor for the full audio spectrum must be also very expensive and maybe hard to find. The challenge is to find a good compromise with the plate voltage and idle current so that the CCS doesn't have to operate at crazy high B+.

[Nick]

Well, its probably easier to wind a choke that a SE OPTX, but yes. The choke does have the half B+ advantage though with is not insignificant. But now there are some 1000v high power depletion mosfets available it may be worth another visit.

[Cressy Snr]

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.

I like to do good job, so did my dad and so does our Ant. I’ve no idea though, how this transformer conversion is going to go, but I can’t help but be fastidious about lining up the laminations dead straight and dead flat, as far as their manufacturing tolerances will allow.
I’ve noticed with the stuff I’ve read about C core SE transformers, that the mating faces of their gaps are ground and polished to a mirror shine, so that the gap is microscopically uniform over its entire surface area. I can’t go to that level with an EI transformer with laminations, but stacking them and lining up the gap mating surfaces on a clean, dust-free mirror will get me a gap with as flat a pair of surfaces as standard laminations will allow.

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….

Thanks Max: a possibility for the future. I need to see what happens with these reassembled transformers first.

[Nick]

that the mating faces of their gaps are ground and polished to a mirror shine

Sounds like bullshit to me. I would think that would more than likely short the ends of the laminations together which would do more harm than good. Also, cant help thinking a bit of variation may be a good thing to soften the onset of saturation. AFAIK, swinging chokes were made with a sloping gap.

Also in use I think the flux will pull the I and E parts together, so leave the bolts loose until its first used.

[Cressy Snr]

Maybe I’m overdoing the attention to detail, but it’ll get done how it gets done and we’ll see what happens.

[Cressy Snr]

that the mating faces of their gaps are ground and polished to a mirror shine

Sounds like bullshit to me…

https://www.butlerwinding.com/c-type-transformer-cores/

https://jandkaudiodesign.blogspot.com/2 ... -core.html

http://jamestransformer.com/en/transfor ... ormer.html

[Nick]

Fare enough, but in each of those cases they are 1. Talking about C core transformers, and b. doing it to minimise the gap because they are not making transformers that see a DC offset, its just the C Core has to be cut to use.

[Cressy Snr]

Well yes, but they still make single ended C core output transformers with shims to create gaps so either way they have to polish the cut ends of the cores. It’s how the cores are manufactured, from what I can see.

Patrick Turner http://www.turneraudio.com.au/se-output ... alc-2.html

If C-cores are used, your calculations will all be different if the C-core has different relative T, S, L, H
dimensions. But if double 00 C-cores did have same dimensions as T51mm x S51mm wasteless E+I,
The initial µ with close butted cores is the maximum possible µ, say 10,000.
Air gap size would be calculated Ag = 280mm x [ ( 1 / 343 ) - ( 1 / 10,000 ) ] = 0.788mm, bigger than
for E+I, and material = 0.39mm for each of the the two gaps in each C-core.

So make sure you see the difference between use of E+I or C-cores. Neither core types are "better" for
OPTs.

So cut me some slack folks FFS! You can see what I’m up against, if you follow the link to Turner’s pages. Some of yous might be mathematical geniuses but I’m certainly not; it’s a struggle, it’s painfully slow, and I’m trying to enjoy the work and come up with something I can make good use of, believe it or not!

Now I did actually try and work out my gap size from his vast tome, just to give me some kind of start. There is nothing below 10W in his examples, so I’ll probably end up having to adjust on test, which seems to be the best policy anyway as both transformers are going to have to have their characteristics matched otherwise the channels will sound different from each other. It’s all very well making/repurposing one, but they have to be repeatable for a stereo pair.
I’ll test things on the one TX I’ve completed tomorrow and see how it measures up. It’ll get a final varnishing process if it sounds any good.

[Nick]

As I say "its just the C Core has to be cut to use". Though I do admit to not reading the C Core part of your post so sorry, I thought I was calling out polishing EI lams.

[Cressy Snr]

...I thought I was calling out polishing EI lams.

Ah....
That's why I couldn't understand your skepticism about C cores.

Anyway I've tested the first one and when you put something in, something comes out. So I'll put the other one together.
I'm being vague because my sig gen is playing up, there's something intermittent going on. Bloody thing keeps stopping and starting at random.

Onwards (sort of)

[Nick]

The mains through a transformer is a good source of sine.

[Cressy Snr]

Thanks Nick,
Never thought of that.

[Cressy Snr]

Both transformers completed:

FBAA640D-471D-46D4-BFB4-C37B875B9404.jpeg (99.76 KiB) Viewed 3786 times

[Ray P]

Well done Steve, looks like a meticulous piece of work you should be proud of.

[Cressy Snr]

Cheers Ray,

In the amplifier and sounding excellent:

A0FC8CB1-E675-4FD9-9AEC-4EFF8873E675.jpeg (106.01 KiB) Viewed 3765 times

To say I’m over the moon with the results would be an understatement!
More of that 45 magic has been let out.
Is there no end to my talents

Alright …alright …I know! I only dismantled, then reassembled them into single ended format; I didn’t actually wind the damn things, I did work out the gap size though courtesy of Mr Turner, so I did at least do something propellerheadish. I doubt if I could do it again. No-one was more surprised than me when they worked first time and produced undistorted bass at top volume. But then again it’s only 1.6W we’re talking about so maybe I got lucky.

Nevertheless, it’s great to hear the results of all that painstaking work with mirrors, varnish, clamps and a rubber mallet to hit myself on the head with, when the maths got on top of me. Thanks for pointing me to the Turner Resource Paul.