Tweet
This amp came to me w/blown mains fuse, and one of the six 100 ohm power tube screen resistors open. I replaced the bad resistor, installed a new set of power tubes, changed the bias resistor to achieve about 52% of max for 6L6GC. Amp came back today, it started smoking...found the 400 ohm power supply resistor looking a bit scorched w/burned PCB underneath, but the resistor still meters @400ohms. What could be going on? Thanks for your help!
-
-
It measures 400 ohms because it is wirewound, Usually it will open, or be OK. It is hot because something downstream is drawing current through it.
If the new tubes are all good, and the 100 ohmers all OK, then check the filter caps on the downstream side of the 400 ohm for excess leakage or shorts.
Also, turn out the room lights and look closely at the tube socket area for any tiny blue sparks, which would be arcs.Education is what you're left with after you have forgotten what you have learned. -
My Classic VT burned the same 400ohm resistor last year. It turned out to be a failing filter cap in the power supply. It's been running fine ever since replacing the caps.Comment
Comment