Variation on Rodīs bias servo - diyAudio
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Old 2nd August 2010, 06:49 AM   #1
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Join Date: May 2007
Default Variation on Rodīs bias servo

In the Spud, Schade, PP, Anti-triode ECL86 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 FETīs 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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Last edited by revintage; 2nd August 2010 at 07:13 AM.
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