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I have a customer who is curious about me building him amp similar to this one:dano_commando.pdf (el34world.com) It's pretty straight forward except for the biasing scheme for the power tubes which to me does not look like a great idea. The cathode of the power tubes runs to the heaters of the 12AX7 which are wired in series to the ground along with a 10uf cap; a odd ball form of cathode bias.
I could be wrong but it seems to me if the you ever had a 12AX7 heater go bad you would have real problem and not develop voltage on the cathode and the power tubes could go in runaway. I'm not sure if this type of bias system has any tonal properties. Does anyone know? Would I be better off making the amp a more standard form of cathode bias or fixed bias?
Thanks for the input!
I could be wrong but it seems to me if the you ever had a 12AX7 heater go bad you would have real problem and not develop voltage on the cathode and the power tubes could go in runaway. I'm not sure if this type of bias system has any tonal properties. Does anyone know? Would I be better off making the amp a more standard form of cathode bias or fixed bias?
Thanks for the input!
