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Symptoms: After playing for a while, gain decreases, muffled output. Upon inspection, V4 output tube appeared hot, with blue glow. Thought bad tube, replaced same result. Checked bias using BiasProbe, bias fluctuates, starts at about 40mV increases to 43mV after few minutes; same thing with V5 tube, bias starts at about 34.2mV increases to 41+; it never settles constantly fluctuates.
Checked voltages and compared with reference voltages obtained from Lee Jackson service DVD.
bias trim ctrl: -62, -41
1.5K resistors: -41, -41
power supply caps: +250, +240, +510, +460, +260
My voltages are slightly lower than the refs on the DVD, but appear within tolerance?
Also voltages at the tube sockets: plate (pin 3) +495, screen (pin 4) +480
I first suspected the screen resistors since they had a dark stripe across their center but they test ~470 Ohms, plus I've seen the same stripe on other mig 50 pics on the internet.
Can someone help troubleshoot? And feel free to correct anything I've said, I've studied a lot, done a lot of things like know how to discharge filter caps, replace pots, etc., but my knowledge level is just enough to be dangerous.
Checked voltages and compared with reference voltages obtained from Lee Jackson service DVD.
bias trim ctrl: -62, -41
1.5K resistors: -41, -41
power supply caps: +250, +240, +510, +460, +260
My voltages are slightly lower than the refs on the DVD, but appear within tolerance?
Also voltages at the tube sockets: plate (pin 3) +495, screen (pin 4) +480
I first suspected the screen resistors since they had a dark stripe across their center but they test ~470 Ohms, plus I've seen the same stripe on other mig 50 pics on the internet.
Can someone help troubleshoot? And feel free to correct anything I've said, I've studied a lot, done a lot of things like know how to discharge filter caps, replace pots, etc., but my knowledge level is just enough to be dangerous.