The right channel is the issue. All the big plate resistors get hot after a few minutes. 130v on one leg, 30v on the other leg
From the working side,
1.What is the voltage across the plate resistors?
2.What is the voltage between pins 1 & 3 of Q12?
3.What is the voltage between pins 1of Q12 and the -15VA rail?
4.What is the voltage across R121?
Do the same for the plate resistors, Q14 and R156 on the faulty side.
1.What is the voltage across the plate resistors?
2.What is the voltage between pins 1 & 3 of Q12?
3.What is the voltage between pins 1of Q12 and the -15VA rail?
4.What is the voltage across R121?
Do the same for the plate resistors, Q14 and R156 on the faulty side.
BTW - I did replace Q14 - no difference
1 12v. Bad side 90v
2 4v. Bad side 10v
3 Measure from pin to ???
4 1.2v Bad side 2v
1 12v. Bad side 90v
2 4v. Bad side 10v
3 Measure from pin to ???
4 1.2v Bad side 2v
Curious how this turns out. I would suspect a shorted IRF620 (Q14). With this shorted, there is about 160R between cathodes (bit above gnd potential) and the -15V supply. This would pull about 100mA through the tubes, 50mA per side. With 1k275 in each plate this is about 60V drop.
Maybe RFBRW sorts this out like this, otherwise it would be great if you could write the measured DC values in the schematic, for both channels. In Post 6 you say 150V on the good, 130V on the bad, afterwards, that there is 12V over plate resistor in the good channel, and 90V in the bad channel, and this does not seems to agree.
Maybe RFBRW sorts this out like this, otherwise it would be great if you could write the measured DC values in the schematic, for both channels. In Post 6 you say 150V on the good, 130V on the bad, afterwards, that there is 12V over plate resistor in the good channel, and 90V in the bad channel, and this does not seems to agree.
Well my first measure measurements were resistor leg to ground. Then when rfbrw asked across the resistor, I actually measured resistor leg to resistor leg
These are both values for the right channel? So 30V over either R141-R144 or R145-R148 and 130 over either R141-R144 or R145-R148?
Did you check if all the R141 to R148 are still ok, or, if the combination of 4 parallel resistors still measures around 1k275? Just thinking if some resistor opened, and the others are taking the burn now...
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The one 130 on one side and 30 on the other is across any of the plate resistors on that channel. Other channel is fine
Have you replaced Q15 ?. I'd try replacing Q15 and VR6. You would expect about 0.7V between Q15 pin 2 and Q15 pin 1. You could do a quick comparison with Q13 on the working side.
I have not replaced Q15. So VR6 is empty. Looks like VR6 and VR3 were there for the design with 6 tubes and this is the 4 tube version. Let me see if I have a Q15 which calls for a 2N5088
but the same schematic was used for a 6 tube version and 4 tube version. So my 4 tube is V1, V3, V4, and V6 on the tubes. With VR2 and Vr5 populated
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