Weird Bias peoblem

[shelby1420]

Ok, finished the second amp without issue, all of my readings were well within 10%, however when I attempted to adjust the bias ( setting it for 477/3 = 159) it won't move from the 61 posted on my meter, no matter if I turn the little screw or not, could it be the bias pott is faulty???

[Paul Joppa]

61v on the plate is too low to be the pot. It could be the 431 chip, but is more likely that the cathode is shorted to ground. That would be pin 2 of the tube socket, or a solder bridge on the 431 chip on the "A" side of the board (K to A terminals, which are adjacent to each other).

[shelby1420]

Brilliant, brilliant I say!!!!  Sure enough I had a wire melted through touching pin 2 of the 9 pin socket, thanks Paul!!!!!