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RE: schematic

The output transformer primary just hooks up where the speaker goes and the speaker hooks up to the secondary of the transformer.

The same idea as Paul's Zero Autoformers only taken to an extreme.


Paul's autoformer is great, it just does not go far enough to load the tubes for real Class A operation. The 3 X hook up will make your 8 ohm speaker look like a 32 ohm load for the amplifier.

I hate to use the term extreme. It's not really. Loading 8 6as7g's in a Circlotron (Atma-Sphere M-60) circuit with 172 ohms is not extreme at all.

It's just proper loading for real Class A operation. It yields 42 Class A watts.

If you remove 4 tubes per amp and load with 325 ohm you get 14 watts all Class A with very low distortion.

You will get less power, much less harmonic distortion and much better damping factor with a transformer.

I think a transformer winder like Heyboer could make any impedance you want.

Talk to Douglas (PakProtector) over in the Tube DIY forum about dealing with Heyboer.

The Freed transformer I'm using came from a Krohn-Hite amplifier with push pull parallel 6550's.

It has four identical primaries that I have wired in parallel and two identical secondaries that are wired in series. That's how I get to a 325 ohm primary with my 13 ohm speakers.

Have Fun and Enjoy the Music
"Still Working the Problem"

Edits: 08/19/11 08/19/11 08/19/11

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