I once experimented with a 6BQ5 amp by replacing one tube with a resistor, which will provide the balance current, but last forever - if the right wattage is used. Didnt think of a way to linearly swing that baby into place, to go from PP to SE through a potentiometer. Maybe do it with PWM and an inverted PWM for the cathode resistor, such that the tube bias's off as the resistor gets shunted to ground.
I've never connected a FET across one of two cathode bias resistors in series - the one going to ground - with a 50% duty 100 kHz signal driving its gate. You? Anyone?
What of using some massive 50 mA OPT with little tubes, running 10 mA? The OPT having enough iron to shrug off saturation in one direction? A waste I know, but - DIY. Where results are preferred over elegance. Made possible by what we happen to have lying around.
I've never connected a FET across one of two cathode bias resistors in series - the one going to ground - with a 50% duty 100 kHz signal driving its gate. You? Anyone?
What of using some massive 50 mA OPT with little tubes, running 10 mA? The OPT having enough iron to shrug off saturation in one direction? A waste I know, but - DIY. Where results are preferred over elegance. Made possible by what we happen to have lying around.