this might be a long one....
its a Sound City Concord combo
(schematic attached)
i inherited this amp from a friend - "if you can fix it, you can have it!" - another mutual friend had worked on it once upon a time with no success.
its already a complicated, cramped mess in there, but add to that the fact that i think the previous 'tech' may have tried out some voodoo of his own, and i really have no idea what's going on.
with a limiter in-line, the pilot lamp lights (dimly) but that's about it. no heaters no nothing. so im stuck at the first step trying to figure out: is the amp getting power? the light bulb does NOT light at all.
here are some brief measurements/observations so far:
1) something weird with the mains switch: the pilot light is hooked up DIRECTLY to the same pin as the "N" mains connection (rather than being on the other side of the switch, as it says in the schematic). on the other side of the switch is a blue wire that goes to a node that goes somewhere into the PT.
2) with the amp turned on (but on standby, of course), and one DMM lead hooked up to the "N" side of the mains, i can read ~120VAC all over the place: both main filter cap terminals, tube heater pins....??
3) the main filter caps have little lumps on the bottom with some white looking flaky residue. i assume that's bad!
4) there seems to be some kind of modification on the output of the bridge....an additional 47nF cap and 22K resistor and another diode....doing something i dont know.
i will go in and do a more careful trace to see what's going on and report back. its pretty confusing and hard to pick apart but ill start with the power section and see if i can at least figure that out.
its a Sound City Concord combo
(schematic attached)
i inherited this amp from a friend - "if you can fix it, you can have it!" - another mutual friend had worked on it once upon a time with no success.
its already a complicated, cramped mess in there, but add to that the fact that i think the previous 'tech' may have tried out some voodoo of his own, and i really have no idea what's going on.
with a limiter in-line, the pilot lamp lights (dimly) but that's about it. no heaters no nothing. so im stuck at the first step trying to figure out: is the amp getting power? the light bulb does NOT light at all.
here are some brief measurements/observations so far:
1) something weird with the mains switch: the pilot light is hooked up DIRECTLY to the same pin as the "N" mains connection (rather than being on the other side of the switch, as it says in the schematic). on the other side of the switch is a blue wire that goes to a node that goes somewhere into the PT.
2) with the amp turned on (but on standby, of course), and one DMM lead hooked up to the "N" side of the mains, i can read ~120VAC all over the place: both main filter cap terminals, tube heater pins....??
3) the main filter caps have little lumps on the bottom with some white looking flaky residue. i assume that's bad!
4) there seems to be some kind of modification on the output of the bridge....an additional 47nF cap and 22K resistor and another diode....doing something i dont know.
i will go in and do a more careful trace to see what's going on and report back. its pretty confusing and hard to pick apart but ill start with the power section and see if i can at least figure that out.