Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: jaster55 on December 23, 2016, 11:54:01 pm
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This is my first Hoffman build. I just finished a princeton reverb and after thoroughly checking everything over I am about to fire it up...
I am a bit confused on how to set the negative bias voltage to max.The instructions say turn the bias pot so that pin 5 on the power tubes has the most negative voltage. I'm sure the reading is taken between pin 5 and ground but it doesn't indicate that in the article and I just want to be sure.
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Clip your (+) meter probe to pin 5, (-) to ground, power it up with no tubes, turn the control, and you will read in your meter, which direction is more negative.
Edit:
Never mind. Your first build should be powered up with light bulb limiter. You might have a firework display there. Use your meter reading ohms from pin 5 to ground. Turn the pot and see which direction goes more to ground. That is the least negative direction.
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... I am a bit confused on how to set the negative bias voltage to max. ...
Look at your bias pot/trimpot. When you adjust it, you can probably visualize where the wiper travels along the resistive path when the pot/trimpot is turned.
Turn the pot/trimpot so the wiper is at the end closest to the bias diode. That will be maximum negative voltage.