08-08-2017, 04:33 PM
the JCM2000 ( and a few others) have 1 ohm resistors connected to the cathode of the power tubes.
if you want to know the current through a resistor it is I = V/R (in this case R = 1, so the voltage you measure is equivalent to the current.)
The same thing could be done if you added a 1 ohm resistor. I believe the R50H power tubes are PCB mount, which makes things more difficult
the bias probe I linked to has a 1 ohm resistor internally. So it would allow you to measure the bias current on any amp, without permanently installing a resistor.
There is also the possibility that you just measured the bias voltage, which is technically biasing the tube, but not to a known point. it could be exceeding the maximum plate dissipation, in which case you would start to red plate, or it could be biased too cold, in which case it would sound kinda blatty. Theres also the chance that it would fall within an acceptable plate dissipation range and be just fine. but as expensive at power tubes can be, its best to know.
if you want to know the current through a resistor it is I = V/R (in this case R = 1, so the voltage you measure is equivalent to the current.)
The same thing could be done if you added a 1 ohm resistor. I believe the R50H power tubes are PCB mount, which makes things more difficult
the bias probe I linked to has a 1 ohm resistor internally. So it would allow you to measure the bias current on any amp, without permanently installing a resistor.
There is also the possibility that you just measured the bias voltage, which is technically biasing the tube, but not to a known point. it could be exceeding the maximum plate dissipation, in which case you would start to red plate, or it could be biased too cold, in which case it would sound kinda blatty. Theres also the chance that it would fall within an acceptable plate dissipation range and be just fine. but as expensive at power tubes can be, its best to know.