multiple independent grid biasing from 1 mosfet

[exeric]

In a recent thread parallel output tube advantages and disadvantages were discussed. The thread starter wanted to implement it using mosfet drives (ala powerdrive). Some thought it should be implemented with a mosfet for each driven tube to balance the drive manually. Here is a possible circuit that can balance each tube bias individually and manually while using just 1 mosfet (2 for PP). The rheostats shown could just as easily be potentiometers. Comments welcome.

[leadbelly]

Isn't this only applicable for situations where the grid represents a high impedance? In other words, not A2, AB2, or screen drive, but just good old A1 or AB1 grid drive?

[exeric]

You might be right. I hadn't thought about it correctly. It looked like it would work but it will require some kind of mod that might be much more complicated than it is worth. Maybe someone else can come up with a modification that can make it work without adding more active devices.