I have two model Ts now, both of which I've recapped, neither of which I've had for more than a month. One of them I recapped more recently, and yesterday was the second time I had played it since recapping it. So, I'm playing, hear a pop, and one of the power tubes rapidly gets brighter than the sun. I dive to turn the thing off. Get the chassis out of the head shell, and the problem is pretty clear. The resistor attached to position 4 on that power tube literally exploded (pics below). Upon further investigation, the resistors in position 4 on every tube don't seem to be right. If you look at the highlighted part of the schematic below, position 4 should have a 1.5k 5w resistor. The resistor in this spot is a 47 ohm resistor, and is definitely not 5w from the look of it...it's a simple film resistor, which I don't believe are ever good for more than 1/2w or maybe 1w. For power resistors, they're typically the wirewound variety that look like an elongated sugar cube. I open up my other model t for comparison, and it indeed has the 1.5k resistor in position 4, but in this amp, position 3 has a 50 ohm resistor, rather than a 47 like the schematic says. At 10% tolerance, this doesn't make a difference, but it's still kind of weird. Was sunn really this sloppy? Could they really have installed a 47ohm 1/2w resistor in place of a 1.5k 5w resistor?! Is there any reason there would ever be a 47ohm resistor in this spot? Maybe someone replaced them for a 6L6s or something and didn't know what the hell they were doing...?
Anyway, I replaced the blown resistor with a 50ohm 10w resistor from radioshack, with more resistors in the mail to get the power tube section back to spec. In the meantime, the thing works again with 6550s just fine, but should it be safe with ~50 ohm resistors in position 4? Or should I get it back to spec with the seemingly "correct" 1.5k resistors?
blown resistor:
schematic:
power tube wiring with the mystery 47ohm resistor:
power tube on other model t with correct value resistor:
