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Old 13th September 2012, 05:48 PM   #1
Bigun is offline Bigun  Canada
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Default two amplifiers, one transformer

I'm planning to build a SET and favour the use of a fairly beefy power transformer. I'll be wanting around 500V for B+.

I would also like to play around with some Class A solid state amplifiers. I'd need about the same power rating for the transformer.

Using separate transformers isn't needed as I'll only use one amplifier at a time. And it would save both cost and considerable weight to use only one transformer.

So I thought that if I simply reverse the transformer, instead of 500V output, I will put 120V into the B+ winding and extract a useful 30V or so from the other winding.

I can't see an issue with this, either from a power point of view or safety. But I'd be interested to know if anybody else has some advice on this ?
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Old 13th September 2012, 05:57 PM   #2
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I doubt whether the current rating of the Primary winding would be sufficient for a Class A amplifier.
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Old 13th September 2012, 05:57 PM   #3
Elvee is offline Elvee  Belgium
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It will work, but if you use a transformer at a lower voltage, the series impedance (winding resistance + leakage inductance) will remain the same, and this means the regulation will be very much degraded compared to a regular transformer.
In fact, if you draw the normal current acceptable to the primary (now your secondary), the voltage could be halved or thereabout.
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Old 13th September 2012, 06:24 PM   #4
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if it works. the VA rating will be about 25% of the normal value.
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Old 13th September 2012, 08:57 PM   #5
Bigun is offline Bigun  Canada
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Very helpful response to my question - I'm very glad I asked it ! Thanks.
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