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Original Message
RE: Question re 6BX7GT in 300B push pull designs
Posted by JKT on July 21, 2016 at 15:24:53:
Your concern is well founded. I have such amps, albite PPP KT-120 output stage, and finding 6BX7s with sections matched for bias current (required) in a differential gain stage will be problematic (fortunately I have a goodly stash of them). If you do build these beasts, I would suggest that you consider using CCS fed shunt regs for the input and driver stage B+. For the 6SN7 cathode CCS I would suggest using a cascode BJT current sink a la Morgen Jones. For the output stage use a Fairchild power MOSFET/TL431 cathode CCS. These changes from the original circuit have increased my enjoyment of these amps.