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Old 28th January 2003, 03:20 PM   #1
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Default toroid Transformer as output Transformer for tube preamp?

hi all,
has anyone tried before?
can it be done?

thanks for input..

rgds,
tone
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Old 28th January 2003, 03:27 PM   #2
dhaen is offline dhaen  Europe
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Tone,

There are a number of problems:

They cannot accept any DC, so push pull is essential.
There is barely enough inductance.
The interwinding capacitance is not controlled, so different makes with the same ratings will give different results.

I think 316a has done some work with them. Hopefully he'll reply.

Cheers,
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Old 28th January 2003, 03:34 PM   #3
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Default toroid

hi dhaen,

can a cap at primary winding do the dc job?
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Old 28th January 2003, 03:43 PM   #4
tiroth is offline tiroth  United States
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I know some PP amps have been built with Talema toroids. There is a lot of variation in terms of primary inductance; some toroids are quite high.
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Old 28th January 2003, 03:59 PM   #5
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If u use a parafeed type arrangement you can use toroids..I believe a 50va toroid with a 10:1 stepdown will work..so something like 230v-25volts...
The CCS can be something as simple as a resistor.
Just add a cap in one leg of the primary and voila!

But yes hopefully 316a can shed some more light on the subject.
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Old 28th January 2003, 04:01 PM   #6
dhaen is offline dhaen  Europe
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Tone,

Quote:
can a cap at primary winding do the dc job?
That's a good idea.
Then the primaries could be put in series.

Tiroth,

So desu ka?
I was just wondering whether the smaller ones would have enough inductance. He wouldn't want a 50VA thing in his preamp.
Ja mata.

Of course both ideas depend on the transformer being fed from a sufficiently low source impedance.

I wonder if it worth the trouble. How much does a run - of - the - mill audio stepdown transformer cost in that part of the world?

Kampai,
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Old 28th January 2003, 04:02 PM   #7
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Hi,
have a look here

http://home.t-online.de/home/MHuber/pre-5687.htm

Reg.
Wilfried
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Old 28th January 2003, 04:06 PM   #8
dhaen is offline dhaen  Europe
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wiligruen,

That's elegant.
And a tiny transformer too!

Cheers,
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Old 28th January 2003, 04:29 PM   #9
tiroth is offline tiroth  United States
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dhaen,

Ee. As luck would have it I have a tiny 1.6VA 2:1 toroid (70000 series) and a larger 35VA 27:1 (62000 series) arriving Thursday. I'll measure the primary inductance and report back.
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Old 28th January 2003, 11:06 PM   #10
SY is offline SY  United States
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Tone:

Major dumb question: what are you trying to accomplish? I've always found it useful to define a problem before trying to evaluate solutions.
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