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Fender bassman 300 Pro Bias question Need to know if it is safe to use

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Nighttrain1127:
The Manual and the back panel say to set the bias at 100mV and the Balance at 0mV. So Go to set the Bias and it comes up -100mV. Is it the same either way? Or Is there a Problem? Also it does not say But I am guessing the center connection that is used for both settings is common?

Any Help would be appreciated

Nighttrain1127:
  So I guess it is just a matter of putting the probes into the opposite socket to get the right answer.

Psycho Bass Guy:
Bias is a negative voltage. You WANT a negative reading.

amptech:

--- Quote from: Psycho Bass Guy on May 01, 2017, 09:54:34 PM ---Bias is a negative voltage. You WANT a negative reading.

--- End quote ---

Does these amps actually have a test/set point where you actually measure the bias voltage?
I would think (not familiar with the amp, though) the test points are cathode current.

-100mV of bias voltage just seems a tad too hot :)
 

Psycho Bass Guy:

--- Quote from: amptech on May 01, 2017, 10:29:18 PM ---Does these amps actually have a test/set point where you actually measure the bias voltage?
I would think (not familiar with the amp, though) the test points are cathode current.

-100mV of bias voltage just seems a tad too hot :)
 

--- End quote ---
:o Yep!
It's a built-in test point. I completely missed the "mv" and just read "voltage." A cathode reading should be in current, but who knows what amp manuals say nowadays. I had the amp in question's identical-other-than-cosmetics predecessor, the Sunn 300T, and was never impressed with it so I never dug into it, but from what I remember of its bias monitor circuitry, it was a joke and IIRC caused many output stage failures. I do remember having two of them blow up on me when I was trying them out NEW in stores! (Maybe they were biased in mv, LOL)

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