Originally Posted by
Firebottle
The output valve stage needs to be reconfigured from a common cathode circuit to a cathode follower implementation.
The anode load resistor has to be moved to the cathode plus a B+ connection made to the anode (I fit an anode stopper resistor to ensure complete stability).
A blocking capacitor has to be fitted in the grid connection from the volume control and a suitable bias network added.
The cathode to heater rating of the valve needs to be checked against the new bias voltage to ensure safe operation.
The output impedance is reduced considerably, by a factor of 7-10 times depeding on the valve type.
The only downside is the loss of gain that the output stage was originally providing, usually around 6dB.
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