[Amps] Series screen gate design help

[Vic Rosenthal]

I want to update the old-fashioned clamp-tube circuit.

I want to create a solid-state switch that will accept a voltage input (negative, but it 
can be inverted) derived from the rectified grid current of my class-c amplifier. When 
this input is present, I want the switch to connect the amplifier screen to its power 
supply; when it is not, I want to disconnect the screen voltage.

I am thinking of a circuit similar to the series pass transistor that is used in regulated 
power supplies; but of course the transistor will have to be rated to handle the 400V 
screen voltage (the current will be 80 ma). My amp has a separate screen supply producing 
the 400v.

Unlike the shunt clamp circuit, this won't waste power by pulling down the voltage across 
a resistor -- it will just be a switch.

If this makes sense, what would be a good choice for an NPN power transistor, something 
like a 2N3055 with a higher voltage rating, that could do this? Any other ideas? The 
keywords are cheap and available.

I apologize for still living in a world of 6L6's, etc.
-- 
Vic