StepheK, I didn’t realize this amp has a 290V HV secondary until I reread an earlier post. That is enough (meaning not too much) for proper class A operation for a triode strapped EL34 with a 3.2K opt, or a triode strapped 7591 with a 3.2k opt. You could "double" the reflected impedance on the primary as discussed above, but you will get less power by maybe 20% in either output tube scenario, and it won't be running either output tube optimally. So my vote would be to try first leaving the heaters powered from the power transformer’s 6.3 volt winding, convert to SS rectification, and run the opt as a straight 3.2k primary load.
Under those conditions, power output can be expected as roughly 5 watts with an EL34 or 4 watts with a 7591. I prefer the 7591 option because it has easier drive requirements and requires only 0.8A filament current.
With a 7591 with its easier drive requirements, you could even add a touch of plate-to-plate feedback so the amp isn't super sensitive on the frontend. I'd be careful with that though, since the effective load that that feedback connection will place on the driver stage is essentially the FB resistor size divided by the forward gain of the output stage. In parallel with the load the stage already sees in open loop conditions, could make for a difficult load for the 12AX7 to drive into. (I assume it's a 12AX7 equivalent type driver tube).
However, if you cut over the frontend tube to a 12AT7 or something similar with lower plate resistance, it could mitigate some or much of that concern while still giving you decent open loop gain out of that driver stage so that you see some benefits from adding the feedback.
Just some ideas...take them or leave them as you feel so inclined....
