Individual fixed bias and transf coupling

[mashaffer]

As my financial situation improves thoughts turn to future projects. I am in the process of repairing a battery damaged Korg Poly-Six and I will need an amp for it so I figure this is a perfect first tube project.

I have a couple of organ speakers to use (15" and 10" with whizzer cone) so eventually it will be a biamp situation but step 1 will be a full range driving the 10" but it will eventually become the low section amp.

I want to try PP UL with transformer coupling and phase splitting (just cause I like the idea). I would like to use fixed bias so that I can play with various bias levels between class B and A. I am looking at something like the last two stages shown below (preliminary idea not complete circuit).

But... here is the rub. I wanted to have individual bias control (or a balancing setup) so that I can compensate for any unbalance in DC plate current. My first thought was small adjustable cathode resistors to add enough self bias in addition to the fixed to balance the tubes but I fear that the dynamic characteristics of the two tubes would be thrown out of balance especially as overload is approached.

Am I going to have to settle for RC or DC coupling for the last stage (using transformer splitting before the driver) in order to get individual biasing or are there any clever methods out there to get both?

mike

[ray_moth]

Fixed bias would be easy enough if there were separate secondary windings on the splitter tranny, instead of a centre tap.

[mashaffer]

Slap myself on the head. Brilliant of course. Just need to find an appropriate x-former. This gives me a starting point. So output stage should be fairly straight forward.

I think that I ought to shoot for input and driver stages with plenty of extra headroom so that they can be as linear as possible.

Thanks

mike

[mashaffer]

So I am looking for something like the Hammond 124E shown Here right? I am alittle concerned about that min freq. resp. specification. 150 Hz won't cut it. I imagine that the circuit details could move that all over the planet huh? Will need more info from hammond on pri inductance etc.

mike