Tube DIY Asylum

RE: Adjusting Plate Voltage on Preamp Output Tubes

24.205.128.2

In Reply to: RE: Adjusting Plate Voltage on Preamp Output Tubes posted by Maxamillion on June 30, 2009 at 19:50:14

Yes, I have on output tubes, when trying to dial-in Class "A" cathode biased amps. I usually put a 100 to 150-ohm rheostat inline with a fixed resistor, say 100 ohm, while fine tuning the bias to tone (eg: for an amp that calls for a 220-ohm resistor). The fixed resistor in there just in case the rheostat fails or someone (read: me) cranks the thing the wrong way.

Once I'm happy with tone and status of tube, I replace rheostat and fixed resistor with one unit. Check link for rheostats.

As for gain stage tubes, I haven't used a potentiometer. I play the adding parallel and/or series combos until I hit the point I like (I try for midway between saturation and cut-off). Then, measure the resistance of the mess and replace with one resistor of near equal value. I don't see why you couldn't use a pot, though.
http://www.surplussales.com/Potentiometers/Rheostats/PotsRhe (Open in New Window)

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RE: Adjusting Plate Voltage on Preamp Output Tubes - Maxamillion 20:09:32 06/30/09 (0)

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