[Morris Slutsky]

On Sep 27, 5:06*pm, Morris Slutsky wrote:
Output stage schematic: *http://img14.imageshack.us/img14/8218/pseudootl.jpg

Been playing around with this in SPICE. *This is sort of inspired by
Brosie's single ended "power buffer" circuit, only it's push-pull.
Maybe it's sort of like a McIntosh output stage, except that it
doesn't use a separate feedback winding.

What I like about this idea is that it seems like a very easy way to
apply a bit of damping right at the output stage, without worrying
about low-frequency rolloffs and phase shifts during preceding
stages. *Might be an easy way to tame the low-frequency high-impedance
resonance of a loudspeaker. *While it might be difficult to get
sufficient drive with low-gain triode or beam tetrode tubes, it
doesn't look like a difficult problem to drive this circuit using EL84
or EL34 pentodes.

It's also an elegant looking circuit - to actually hook a speaker
right to the tube cathodes, almost looks like an OTL! *I could even
pretend that some of the tube milliamps were directly driving the
speaker, assisted by the transformer secondary.

I wonder why I've never seen this circuit before. *Is there some
reason that this hasn't been used?

I'm a little concerned about stability, about high resonance
frequencies where the transformer induces a 180 degree shift. *Any
ideas how to be safe about this?

Thanks, I look forward to any suggestions or advice.

I have drawn 4 and 16 ohm taps on the secondary, as I imagine that a 4
ohm tap would be a center tap between 0 and 16 due to the square law
of impedance. I hope this is correct.