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So because you have the combination fixed bias/cathode bias you may be ok to run them at that current level.I frankly am confused by it,other than when you do the math it's not bad.
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You are getting 24watts per tube,right? So 70% would be 21 watts if it was just fixed bias with a 30 watt tube. So with that combination you are getting 55ma,right? If it was just fixed bias alone,that would be too hot,but it's a combination of the two so the cathode current reads much higher than you would set it with just fixed bias alone. So you have a fixed bias supply giving a negative voltage to pin 5 and the cathode resistors as well which changes everything.
#Bias amp 1 vs bias amp 2 pro
If it is a pro reverb and it's a Silverface,then it has the bias adjust AND the cathode resistors on the cathodes. Ok.Before we go any further here,we need to know what YEAR the amp is. Hence the use of bias test sockets, so as not to disturb the existing circuitry. If you need to know the current draw of each individual tube, then 2 resistors, one for ea tube, must be used. I.e., each tube will be drawing 1/2 the value you are reading (which is not strictly true unless the tubes are matched). If the resistor is feeding 2 tubes your voltage drop measurement will be double. I.e., don't rely on the color bands or the value stamped on the resistor which may no longer be accurate. Measure the actual value of the cathode resistor. First turn off the amp, etc., and pull the power tube(s). You can just as well read the voltage drop across the existing cathode resistor then divide that by the value of the cathode resistor, to compute the value of the current.
#Bias amp 1 vs bias amp 2 install
You don't need to install a bias sense resistor in the vintage amp. By the clever use of a 1 Ohm series resistor, the value of the voltage drop always equals the value of the current flow within the circuit being measured. It must be in series with the circuit under test. The resistor cannot "hang-off" and be in an open circuit, or part of some other circuit. So the current of the circuit must flow through the resistor to produce the voltage drop. You are measuring the voltage drop across the resistor.