Power transformers

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Paul Barker
Posts: 59
Joined: Sun Feb 20, 2005 10:20 pm
Location: UK

Power transformers

Post by Paul Barker »

Peter of Tribute phoned me last night, I feel a real heal not giving him personal invite to the recent event we had. Now I have to organise something else so he can come. It all happened a bit quick in the end and was a much greater success than I anticipated.

How many years have I been trying to get this 212 project completed? You know all the problems I've had I thinkj I can now trace to bad (industry standard) power transformers. When you start using very high voltages and current a bad transformer puts so much distortion into your amp. Well I hope that was the cause, I've been chasing problems in all direction for years now. The only time the 212 has sounded like a dream has been when I've used a certain fairly good quality transformer which is potted (1850vct 550mA). This however restricts b+ and unless you want to pull a lot of current the power of the 212 is restricted to 12 watts.

It does however at that rating sound like nothing on earth, and creates the impression there is 40 watts behind it.

So I now have a long hard think time before Peter winds a c core power transformer with slight gap overwound 50%. Trouble with these type of plans is as soon as you've ordered the transformer, you change your mind about what you wanted!
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Joined: Wed Feb 02, 2005 10:02 am

Post by jarek »

I have spent considerable amount of time on that myself when designing my iron. What I used was low loss 0.35mm EI150N lamination. The norm for those lams says Bsat=1.7T but I stayed at 1.2T-1.3T max depending on transformer (the bigger the power the lower the B). For the wire I was trying to stay around 1.5-2 A/mm^2, but still the Rdc turned out to be highish for power trannies (data on my pages). When I compared my designs to the industrial standrads I got an oveshoot of 4x on the core X-section 2-3x on the current density. The problem with the C-cores which my winder pointed me to is that getting them quite is a very, very hard job!

So I now have a long hard think time before Peter winds a c core power transformer with slight gap overwound 50%.
:?: what's that & what for ?


PS The advantage of C-core is that you can change bobbins relatively easy.
Ed Sawyer


Post by Ed Sawyer »

There's a wide selection of nice vintage power trannies out there. I have been slowly picking them up and hoarding some. Good stuff, some potted, in the 1500 - 6000 vct range, @ 200-500ma. Generally they go cheap since they are heavy and insane voltages, so most people dont' have a use for them. Any thoughts or experiences with that sort of thing? Brands like UTC, Chicago, Western Electric, et al.

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Joined: Fri Jan 28, 2005 9:44 am

Post by shinebox »

Allo Paul,

Glad to hear things are getting sorted out.

An air gap and more turns than needed to run the B lower are both mandatory for quality mains iron, as is an e-screen.

Wish all these had occurred to me (the gap in particular) when I spec'd my monster mains tx a while ago... what was that about changing one's mind continuously?

Speaking of which, you are welcome to borrow it if you can collect it! It's (from memory) 4200V centre tapped, few hundred mA, electrostatic screen. Ie perfect for a killer (bad choice of words) 4212 amp... I might want to shove some potting compound in places to help the safety issue.

Never had the nerve to fire it up and I'm putting the monster ESL amp on hold for a while - will try and get something simpler running for the horns first.

Actually, managed to get some R120s (I know, I know, but it's my first tube buy in a while) so I can run off LT *and* use a certain Dave's 5K opts... about bloody time I had some intact iron.

Send my best to Pieter and will give you a shout soon to catch up and hear all about the WAD event.


PS Just reread your post... why not shove a bridge on that power transformer to double your volts and check out the 4212 at HT?
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Joined: Wed Feb 02, 2005 10:02 am

Post by jarek »

An air gap and more turns than needed to run the B lower
You are able to lower B so much that you get one quadrant operation? Otherwise whats the sense of the gap? Hot Barcelona air has probably melted my brain...useless anyway.

Paul Barker
Posts: 59
Joined: Sun Feb 20, 2005 10:20 pm
Location: UK

Post by Paul Barker »

Thanks Chris maybe.

Time we had a session, maybe in the Spring? Will the time ever be right?

Can't get your statics out of my head, are you still persuing those?
Paul Preston
Posts: 1
Joined: Sat Jun 17, 2006 8:46 pm

Large Power transformers

Post by Paul Preston »

Hello all

My first post on the forum. I came past these pages after looking around for info on amorphous transformers.

I could not resist looking in the power transformer pages because I have some experience of large power transformers.

I have for some years been using a pair of parallel single ended 211 amps in my home theatre system. These amps started life in 1995 and evolved into their present form in 2002 and have been unchanged since.

These amps are direct coupled and need a 1500V supply. I tried various HT supplies starting with solid state and voltage doublers. For the last 10 years I have been using a very large RCA transformer (which is a problem to lift). This transformer is centre tapped at about 1750-01750V and I run it through a pair of large mercury vapour recirifiers into an LCLC filter.

The mercury recitifiers and huge transformer have given me the best lf dynamics and gives much better detail on female vocals than using smaller transformers or other styles of HT supply design.

Only thing is the transformer does not have an electrostatic screen. In general, I have found amps with electrostatic screens are much better so I wonder about new HT transformers. But I am reluctant to give up these huge blocks of iron. I can vary the HT load up to 3kW and there is no voltage drop. This happened once when I mistakenly left 211 grids disconnected .

All experience of large HT transformers would be appreciated.

Paul. :?
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