I'm accumulating bits and pieces to build a single tube power stage around a 6AQ5A. I'm contemplating some kind of selector to chose between a solid state rectifier bridge and a 6X4 tube rectifier.

The neat part of using a 6X4 as the power supply rectifier is the fact that the heater filament is separate from the cathode. This allows using a separate (filtered DC?) heater supply.

A nice feature of the 6AQ5A is the nearly linear relationship between plate voltage and cathode bias voltage. I think if I make judicious choices in plate and cathode resistor values, I can set up a Class A self-bias circuit that will perform well over a wide range of line voltages.

I contemplate having a fixed 6.3 VDC heater filament supply and a variable plate supply.

I'll be using a Peavey Rock Master preamp with whatever power amp I come up with. This gives me the option of using either a 1 Volt or 3 Volt nominal drive level to the power stage.

I have an RCA Electron Tube Handbook (circa 1953) which shows the 6K6GT in a single-tube cathode bias circuit rolling off from 3.4 Watts at 250 Volts on the plate, to 0.35 Watts with 100 Volts on the plate. The bias values track as a percentage of the plate voltage (-18V & -7V). I don't know if the sound would be noticeably different from the beam power tubes or not. Looks good!

I chose the 6AQ5A simply because I have a bunch of them, and I can easily accomodate a 6V6 by installing a larger socket.

Its so nice to hear from someone who knows tubes!

[Edited by Lordathestrings on 09-26-2001 at 11:28 PM]