SET Asylum

Single Ended Triodes (SETs), the ultimate tube lovers dream.

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Original Message

RE: The answer is no

Posted by Tre' on September 4, 2017 at 07:45:30:
"Things that happen simultaneously in degrees aren't
well explained with absolutist calculations."
Yes they are.
As the frequency falls the reactance of the capacitor increases and more of the total current flows through the resistor.
If we want 20Hz to flow only through the cap (and not cause current feedback to be applied to the tube) then we design the filter so that it's -3db point is a decade below 20Hz.
With a -3db point of 2Hz the phase and amplitude will be back to flat by 20Hz and virtually no AC will be flowing through the resistor.
What is the -3db point of the filter created by the (cathode resistor in parallel with the cathode impedance) and the value you picked for your cathode bypass cap.
If you give me the numbers I can show you how much of the AC is going through the resistor at any frequency you're interested in.
I can even tell you how much negative current feedback you are applying to the output tube at any frequency you're interested in and how much that increased the output tube's plate resistance and what that does to the damping factor of the amplifier.
All of these complex situations are easily explained with absolutist calculations.
BTW whether you know it or not it's that local current feedback that gives you the sound you are looking for. Your circuit design is technically wrong but you won't admit that. The fact is you're just building for a sound, an effect.
That's OK, we probably all do but most of us admit to it.
Tre'