• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Pentode with high G2 rating ?

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PRR

PRR

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IslandPink said:
...a power pentode or tetrode with a higher G2 voltage rating ... approx. 700 to 750V ... to run about 50mA....
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You want high G2 voltage for high cathode current.

Assuming ordinary tubes, as you say you can only run 50mA at these voltages.

A 6550 with 250V on G2 can pass >300mA. If you only need 50mA, you can drop Vg2 down to 72V. This also reduces Vg1 swing needed, increases the stage gain, and reduces Ig2 to just a few mA. Maybe low enough you can get your 75V-100V Ig2 from a resistor bleeder.
 
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