• 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.

Direct Coupled Amp

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Can I use fixed bias on a direct coupled KT88 single ended amp i'm working on and use an anode load resistor to drop the voltage for the input stage?
What sort of negative voltage am i looking for to bias the KT's?
I would be extremely wary of this approach. At least with cathode bias the KT88 is less prone to run away, though the drifting driver still makes this a possibility. With fixed bias the driver will drift as well as the Output - and if they both drift in the wrong way your KT88 will run away and melt.

A solution to this would be to use a CCS as your bias element on the KT88, this way it will never melt and will stay in correct adjustment whatever the driver does. However you need a large cathode bypass cap for this to work.

Shoog
 
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