In the http://www.diyaudio.com/forums/tubes-valves/151220-spud-schade-pp-anti-triode-ecl86.html thread Rod Coleman suggested a very nice and practical bias servo.
With the help of a sensingresistor in the anodecircuit a simple single-transistor servo was made that levelshifted down to a suitable level.
When using a servo a mains toroid can be used as OPT.
In this one a DC-connected 6S45 is used as a single driver . To phase-reverse the signal for the other output tube a Schaded depletion-FET(pref.IXTP01N100) is to be used.
By combining Rods servo with an OP-amp integrator, for both phase-reversal and filtering, and sending the correcting-voltage back to the FET´s gate everything seems to work in theory. R18 is used to set initial balance. Will this work IRL? It might maybe be some time-constant issues.
With the help of a sensingresistor in the anodecircuit a simple single-transistor servo was made that levelshifted down to a suitable level.
When using a servo a mains toroid can be used as OPT.
In this one a DC-connected 6S45 is used as a single driver . To phase-reverse the signal for the other output tube a Schaded depletion-FET(pref.IXTP01N100) is to be used.
By combining Rods servo with an OP-amp integrator, for both phase-reversal and filtering, and sending the correcting-voltage back to the FET´s gate everything seems to work in theory. R18 is used to set initial balance. Will this work IRL? It might maybe be some time-constant issues.
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