circuit design changes

 Before even starting to build the electronics portion of this amp, already I'm contemplating some changes.

First, and simplest, I'm going to add an output jack to the AB763+ preamp.  This will be a simple, non-switching jack, always active regardless of the position of the preamp select switch.  This will allow the preamp to be used independently as a general processing element -- including, it will thereby be possible to patch the AB763+ preamp into the input of the VTX preamp, with a cable, thus duplicating my typical amp configuration of old, where I'd put a tube preamp in front of a Peavey solid state preamp for more and better gain.

In a more significant change, I'm now thinking I will configure the power amp as cathode-biased, with the simpler and more primitive one-triode phase inverter (what's it called?) rather than the long-tailed pair.  This will free up a triode section to become a switchable boost stage, which I've wanted.  These changes will both tend to reduce the maximum wattage output, which is a benefit more than a problem.  I'm kind of scared of "fixed" bias (i.e., adjustable bias in fact).  I don't like having a trim pot with a "destroy tubes" setting, one inadvertent twiddle or vibration-induced motion or component drift/failure away from catastrophe.  This will make the power amp circuit somewhat similar to the Fender Tweed Deluxe, 5E3.  These normally didn't have NFB, but Rob Robinette shows how to add NFB to a 5E3, which I think I can roughly duplicate, also adding my presence and depth (resonance) knobs as originally planned.

(They're called cathodyne phase inverters.)

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