I'm working on a project and I need some assistance.
I have an audio tube amplifier output stage that I need to have adjustable operating points while maintaining a DC null at the output.
[![enter image description here]] As you can see it's a white cathode follower with a DC offset servo to null the output. I need to be able to adjust the load line but if I adjust the operating point I must also adjust the servo offset.
R12 is the variable resistor to set the CVS voltage but in order to maintain 0vDC on the output of the amplifier and keep the current of the tubes balanced I need to decrease the negative supply voltage of the servo when I increase the resistance of R12 and I need to increase the supply voltage of the servo when I decrease the resistance of R12, up to -300v. Sadly opamps with the required supply voltage and output swing don't exist unless you want to pay $500
So I have 2 problems, I need to have some sort of servo that will adjust the supply voltage of the DC offset servo as I change the resistance of R12 and I need to figure out an alternative way to an opamp for use as a DC offset servo since no opamp worth paying for is going to handle the needed voltages.