DC gain

Thinking more about this DC gain issue.  If, indeed, what is needed to create the magical fuzz effect is relatively high DC gain, well, I sure don't have it.

The innate DC gain of each of my tube stages is right around 1.  But then, I run through resistor dividers: one between the two sections, and the other (effectively) in my variable-bias circuit.  In each case, the divider is acting as a level-shifter, to bring the high DC level of the plate outputs down to the bias voltage required on the grids, which is considered to be roughly 4 volts below the cathode voltage.  That's why I'm running the tubes with large cathode resistors, to raise the target grid voltage up to closer to the plate voltage.  But nonetheless, the target voltage will always be well below the plate voltage, since the plate-cathode resistance of the tube is effectively somewhere around 60k.  So I need to shift the levels downwards, but the gain-reduction of the resistor ladders is an unfortunate and undesirable side-effect.  Each one divides by 2, so overall, my DC gain is probably around 0.25!

So.  One possibility, keeping the circuit all-tube, would be to use tube rectifiers as diodes, which would give a level-shift of perhaps up to 50V.  Maybe I could even use 12AX7 stages as rectifiers, I don't know; probably.  But actually, the easy way to at least test the validity of this idea, would be to use Zener diodes.  They have these up to rather high voltages, like 50V and maybe more.  Given that the diodes would always be conducting, i.e., not acting as clippers or any such, I wouldn't have a "philosophical" objection to using them thusly.  Given enough level shift through this methodology, I could then run the tubes with more conventional small-value cathode resistors, thus obtaining healthy amounts of DC gain.


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