This is for anyone familiar with the Manley Vari-mu stereo compressor. The version I have is one of the early versions (pre REV3) that uses 3 power transformers total , 1 for the A+, filaments and -15V and two independent ones for the B+ on each channel.
The problem I was encountering was that the B+ on the left side was always 30+ volts lower than the right side, which measured correct (390VDC), and this was measured with the entire unit fully unloaded (all tubes pulled), including disconnecting the meters which share the A+ and B+ supplies.
Next I pulled the bridge rectifiers and saw the same thing:
right side PT (unloaded, rectifier pulled): 313 VAC
left side PT (unloaded, rectifier pulled): 275VAC
That's a 38 volt difference.
I cannot think of anything else to account for these differences other than it being due to the transformers having different specs.**
The right side PT is an MCI 4-05-3609, just as specified on the (REV3 & REV5) schematics, and gives the correct voltage
The left side PT is an off the shelf Stancor LB-12230 , and, as far as I can tell, it was in there when it left the factory.
The unit was an early one from the mid 90s, one owner, serial #: MSLS121A
Just curious if anyone else has encountered this in a Manley vari mu?
** For the possibility that the Stancor unit was damaged, I have seen overcooked tube PTs show a lowered unloaded AC voltage, but for those couple of ones that did that, they both dropped drastically when loaded, fully revealing the damaged condition. Same for damaged filament windings - they will read normal for the unloaded condition, then give virtually no output when under load. The Stancor in this unit maintains what is measured in the unloaded state = you get the expected DC voltages under full load, and they are 30+ volts lower than the right under all equivalent conditions (tubes swapped multiple times and tested with tube tester etc) . So at this point I'm inclined to suspect a QC error at the factory, or at least that's what I'd call it, all things considered.
The problem I was encountering was that the B+ on the left side was always 30+ volts lower than the right side, which measured correct (390VDC), and this was measured with the entire unit fully unloaded (all tubes pulled), including disconnecting the meters which share the A+ and B+ supplies.
Next I pulled the bridge rectifiers and saw the same thing:
right side PT (unloaded, rectifier pulled): 313 VAC
left side PT (unloaded, rectifier pulled): 275VAC
That's a 38 volt difference.
I cannot think of anything else to account for these differences other than it being due to the transformers having different specs.**
The right side PT is an MCI 4-05-3609, just as specified on the (REV3 & REV5) schematics, and gives the correct voltage
The left side PT is an off the shelf Stancor LB-12230 , and, as far as I can tell, it was in there when it left the factory.
The unit was an early one from the mid 90s, one owner, serial #: MSLS121A
Just curious if anyone else has encountered this in a Manley vari mu?
** For the possibility that the Stancor unit was damaged, I have seen overcooked tube PTs show a lowered unloaded AC voltage, but for those couple of ones that did that, they both dropped drastically when loaded, fully revealing the damaged condition. Same for damaged filament windings - they will read normal for the unloaded condition, then give virtually no output when under load. The Stancor in this unit maintains what is measured in the unloaded state = you get the expected DC voltages under full load, and they are 30+ volts lower than the right under all equivalent conditions (tubes swapped multiple times and tested with tube tester etc) . So at this point I'm inclined to suspect a QC error at the factory, or at least that's what I'd call it, all things considered.
