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RE: What's the advantage?

Posted by Tre' (P) on September 29, 2009 at 10:26:52

In Reply to: RE: What's the advantage? posted by 6AS7_6SN7 on September 28, 2009 at 23:43:08:

"No adjustments of PP bias currents, no trimmers, 'eternal & perfect' balance of output currents (as the transformer primaries are in series), no need for tube matching..."

Only in terms of saturation of the output transformer. The current, in the output tubes, will still need to be matched if you want the signal waveform to be right.

Also, your output tube cathode bypass caps are 100% in the signal path.
With normal Class A PP that cap is not even needed. (although most put them in anyway)


"Last but not least, you can use economic AC mains transformers (the same as for linear power supply) instead of expensive audio transformers (because of the perfect balance of the bias current)."

Again, only in terms of the output transformer not saturating because of DC.

How good the frequency response of that transformer is has to do with more than just core saturation.

As for "no HT transformer".

1. It forces you to add an input transformer. BTW if you are going to do that anyway, why not make it the phase inverter? A transformer with a center tapped secondary will be a better phase inverter than one built with a tube.

So, input transformer and a 12at7 diff amp to the output stage.

2. It looks scary to me. I like the main rail to be isolated from the wall.

One last question. Why 6as7? There are much more linear tubes you could use.

Tre'


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