Screen grid regulation requirements in Class AB

[Lingwendil]

So, no stabilising but not varying with signal, use a capacitance multiplier to feed the screen.
Mona

+1

Mosfet cap multiplier is cheap and very effective for this, sounds good too. A zener string as a reference is plenty of stabilization for screens on all but the most demanding applications.

 

[obseedian]

I use a tube-based regulator with a triode-connected 6P3S-E as the series pass tube for four KT88 in parallel PP. It gives me about 100 mA of peak screen current with B+ of 440V and screen voltage of 270V. Beyond 100mA the regulation is lost and the pass tube acts like a resistor, giving some measure of protection to the output tubes to prevent excessive screen current especially when the amp clips into high impedances. The only downside is the clipping is not as clean into higher impedances. Clipping into lower impedance is actually smoother since it happens above the knee at higher plate voltage where screen current is lower.