Marcomel79
Well-Known Member
I thought about it as well. If you have a spare 220K resistor i would take that out and replace it
Completely Out of My Depth - Modulus 50w 69 Build
- Thread starter kingfredward
- Start date
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This is a valid question: Is the bias circuit grounded at all?
Looking at the picture in post #181, I can't see if the black wire is soldered to any lug (or where it is connected at the other end, of course)
I went through a calculated the voltages back from the DC current across there 15K resistor - in short they don't marry up. Even when taking when given a rough finger in the air averaging on the meter.
My thinking was from that - the DC current flow is 0.4mA which is quite low but not unheard of. However when you caculate back on the schematic you're about 110V short.. a higher current would resolve this drop 'gap'.
I would be reasonably comfortable with the 352V measurement if there was a low current. That's only 10% above the transformer, and both averaging high (can be 10% high or 60% low - which seems unlikely!) and transformer tolerances (can be ±%) leaves the other option which logically would be a low loading of current or higher wall voltage.
It's either that or the CT on the PT secondary is badly grounded but that would cause issues on the rest of B+..
My thinking was from that - the DC current flow is 0.4mA which is quite low but not unheard of. However when you caculate back on the schematic you're about 110V short.. a higher current would resolve this drop 'gap'.
I would be reasonably comfortable with the 352V measurement if there was a low current. That's only 10% above the transformer, and both averaging high (can be 10% high or 60% low - which seems unlikely!) and transformer tolerances (can be ±%) leaves the other option which logically would be a low loading of current or higher wall voltage.
It's either that or the CT on the PT secondary is badly grounded but that would cause issues on the rest of B+..
Pete Farrington
Well-Known Member
Ill open up my jmp later today and do a comparison. Maybe @Pete Farrington can give us his opinion?
Exactly, my guess is a connection between point 5 and the circuit common chassis is missing.
Marcomel79
Well-Known Member
Dont worry man, well get your amp up and running! But i bet youre gonna pace yourself on the next build 
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