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In Reply to: RE: The amp is a Futterman type if I recall right. posted by si_shami on January 24, 2014 at 11:13:38:
Given the information that there are single bias and balance controls for each channel, it cannot be possible to adjust voltage across each cathode resistor, especially given that there are 30 output tubes!!! So that question is answered.The remaining question is where to set bias. You might start by looking at the parameters of a 6C19. The total bias voltage (or current) will be the sum of what is an acceptable steady-state plate current for a single 6C19, multiplied by 30. It is probably OK to choose a current that is 50% or 60% of what is shown on the data sheet as "max plate current". (I am assuming that the voltage is measured across a single resistor to result in a certain total current. If you can open the chassis and determine the value of the resistor, then we can estimate total current. Look for a resistor with taps on either side of it that go to the taps where bias V is measured. It works by Ohm's Law, V = current X resistance. Only here rearranging to Current = voltage/resistance.
Ralph, please check my reasoning to be certain that I am not misleading Si. Thx.
You might get a clue by measuring the Bias voltage as it is now set. Probably that puts you in the right ballpark. We can go from there, once you've measured that resistor so we can determine total current.
Edits: 01/24/14
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Follow Ups
- RE: The amp is a Futterman type if I recall right. - Lew 11:26:24 01/24/14 (1)
- I would expect a resistor for each tube. - Ralph 13:05:06 01/24/14 (0)
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