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RE: Too low plate R value for a triode ? and CCS substitution?

To the point I made that 80V seems kind of low, I have a Sun 2A3 amp that I modded with CCS loads for the input and driver stages. I kept the input tube 6SN7 but changed the driver to a 6BX7. Because of voltage constraints I had to run the BX7 at 120V p/k instead of the more usual 250V - 300V. Still, with the CCS load the amp sounded very good; much better that stock. One caveat: as the tube ages the plate voltage will increase (bias current fixed by the CCS and thus the bias voltage across the cathode resistor too). As emission falls plate voltage must increase to maintain bias current. This will "eat" into the signal voltage headroom. This can be compensated for by small tweaks to the CCS (decreasing the current). In my case this is critical, in yours maybe not so much if you have lots of extra headroom to begin with.


"It is better to remain silent and thought a fool, then speak and remove all doubt." A. Lincoln


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