My next build is going to be a fixed bias class AB using toroidal OPT's. I would like to use a balancing servo circuit to ensure matched DC current at all times. Can anyone recommend a servo circuit for this? I was thinking of designing one which uses current sense resistors and a high voltage Opamp to bias 1 of the tubes to match the other. But wanted to see what other ideas people have come up with first.
Another possibility would be to use a current mirror on the cathodes, but this would make the amp combination bias, which I would like to avoid if possible.
Another possibility would be to use a current mirror on the cathodes, but this would make the amp combination bias, which I would like to avoid if possible.
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I have a board drawn up implementing a bias servo for balancing two tubes (You set one tube with a pot and the other follows). I used a Broskie circuit. It is similar to the "The Emperor's New Amplifier" servo, but Broskie correctly balanced the time constants in the two low pass filters on the inputs of the op-amp.
Broskie did a couple of autobias articles and then a balance servo for a push-pull output stage. Let me know if you can't find it.
Broskie did a couple of autobias articles and then a balance servo for a push-pull output stage. Let me know if you can't find it.
Amplifier auto bias circuits: Alan Dower Blumlein's garter circuit
He continues for a couple of blog entries before getting to the class AB circuit.
He continues for a couple of blog entries before getting to the class AB circuit.
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