Bottlehead Kits > MonAmour
Bias and Meter Reading Slightly Off
RdDgWest:
I'm at the Bias and Meter Test stage of the build.
Good news is both meters work and perform virtually identically.
When the switch is in the 50mA position the meter goes to the first mark to the left of the 40mA indication on the meter.
When the switch is in the 60mA position the meter goes to the first first mark before the 60mA indication on the meter.
Just not sure what could cause both meters to be off this way and not aligning with the build manual. Open to ideas to check.
Paul Birkeland:
You'd want to report the DC voltage on the center lug of the hum pot in both positions to know with absolute certainty. There is also a slotted screw on the front of the meters that can be used to fine tune the meter to the actual current reported, as there will be some variations in the 9.09 resistors soldered across the meter.
Although there have been many reported issues with the meters, the last batch I got back all tested fine and went into my own projects, so a proper debugging seems like a good idea.
RdDgWest:
Thank you Paul
Measurements from one of the amps (right)
50mA switch position - Center pin of hum pot = 64.1VDC
60mA switch position - Center pin of hum pot = 59.3 VDC
Paul Birkeland:
Can you also do a DC resistance measurement between ground and the center lug of the hum pot in both positions? That would enable me to give you the most accurate information. It will take your meter a few moments to stabilize in the presence of the cathode bypass capacitor, but it should still provide an accurate reading.
RdDgWest:
Thank you Paul
50mA switch position is 1.18K - Current would be 64.1V / 1.18K = 0.054A
60mA switch position is 0.910K - Current would be 59.3V / 0.910K = 0.065A
I have this correct?
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