Hello all
So I have been playing with this amp for a bit and reading the fourth edition of Valve Amplifiers. I have finally gotten the output to be a decent voltage without distortion. However I am running into the issue that lower frequencies really drop in voltage and the higher frequencies spike. cant seem to figure out how to address this, any advice will be appreciated, if my design sucks, please tell me.
So I have been playing with this amp for a bit and reading the fourth edition of Valve Amplifiers. I have finally gotten the output to be a decent voltage without distortion. However I am running into the issue that lower frequencies really drop in voltage and the higher frequencies spike. cant seem to figure out how to address this, any advice will be appreciated, if my design sucks, please tell me.
F=1/(2πRC) . So 10nF loaded by 250K is a 64Hz high-pass filter, 10nF loaded by 20K is a 796Hz high-pass, by 5k is a 3183Hz high-pass, by 400K is about 40Hz, and by 750K is about 30Hz. But the plate impedances will add to the total resistance so it should not be that bad. Historically, 10nF was used with 1Meg for about 15Hz up. And the following grid resistor should be larger than the plate resistor to avoid wasting signal by loading, but not too large for the KT88 grid. Typical amps used 100K on the output grids and 100nF, for about 15Hz. So the driver plate resistor needs to be less than 100k, say 22k, and ample driver plate current (=small cathode resistor). Tube amps were largely rule-of-thumb and copied from one to the next, including some bad ideas.
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