Matchless filament voodoo

[alexradium]

"Why do you suspect the mosfet?"

Because it's a simple circuit, and signal stops at the gate. Haven't pulled it to measure yet. Not sure which version of this circuit I have, there are some different ones, or I would post a schematic. Basically, input passes thru a cap, there is signal on one side, not the side that connects with MOSFET gate. In circuit diode test reads have my meter chirping like a bird.

Mostly interested in the lamps function in life.

that mosfet needs a zener protection,that's why sometimes it fails,and maybe a resistor in series with the gate.

[Randall]

Turns out this is a "very custom build" by Phil Jamison at Matchless. I managed to get a little screwdriver in and flip that footswitch, and now the amp functions. Phil commented that he would not have put that box in there, but that's what the guy wanted. Plus it was turned full up. My customer took it home to see how he likes it now without the mod. He's a purist of sorts, so I imagine he will like it as it was intended. Stranger one this was.

[nosaj]

Turns out this is a "very custom build" by Phil Jamison at Matchless. I managed to get a little screwdriver in and flip that footswitch, and now the amp functions. Phil commented that he would not have put that box in there, but that's what the guy wanted. Plus it was turned full up. My customer took it home to see how he likes it now without the mod. He's a purist of sorts, so I imagine he will like it as it was intended. Stranger one this was.

Wonder who hit the switch? Guess it wasn't the fet at all
nosaj

[The Dude]

My guess is that the FET is bad and that flipping the switch bypassed the effect taking it out of the circuit.

[nosaj]

My guess is that the FET is bad and that flipping the switch bypassed the effect taking it out of the circuit.

That's very probable I should've' thought of that. Signal trace would've told us for sure.
nosaj

[Randall]

It definitely true bypassed the failed board.