Bugera 1960 NON infinium

[Helmholtz]

The mains fuse blows within seconds of the amp being fully on, as in the standby in the play position.

So that's (only) with power tubes in?

Also, I measured the 220k ohm resistors (R15 and R23) one of them read 220-ish k ohms, the other one reads ~ 680-ish k ohms

Is that with the resistors out of circuit?

Detailing matters, even seemingly redundant info might be helpful.

[Danglin' Fury]

It blows with the power tubes in but it does NOT blow the mains fuse with the power tubes removed... I changed the resistors....(r15 and r23) and no joy. I get anywhere from approximately 20vdc to 35vdc on pin 5 of the right 2 EL-34 sockets (looking at the chassis from the back) as I sweep the bias pot. The left 2 sockets read steady at 1.43 vdc. It does not sweep with the turning of the bias pot... all of this is with the power tubes out.

[Helmholtz]

Try what I suggested in post #14.

What does the bad 220k resistor measure out of circuit?

What resistance do you measure between right and left side socket pins 5?

What is the voltage at the bias test point?

[Danglin' Fury]

I will pull the leg of those caps at my 2:30 break.
both r15 and r23 measure ~218k ohms out of circuit.
Pin 5 of the right pair to pin 5 of the left pair I get ~ 283 k ohms.
-27-ish Vdc at the bias test point.

[Helmholtz]

I will pull the leg of those caps at my 2:30 break.
both r15 and r23 measure ~218k ohms out of circuit.
Pin 5 of the right pair to pin 5 of the left pair I get ~ 283 k ohms.
-27-ish Vdc at the bias test point.

THat's all very confusing.
Resistance between left and right side pins 5 should be 440k with good and well connectted R15/R23.
Voltage value at the bias test point shouldn't be lower than any of the pin 5 voltages.

I hope you're not measuring resistances with the amp powered.
Is your meter/battery good?

[Danglin' Fury]

My meter is a perfectly working Fluke 87 V, I am not measuring resistance with the power on. Battery is good....

[Helmholtz]

If disconnecting the coupling caps makes no difference to the pin 5 voltages, you might have a leaking (carbonized?) tube socket.

[Danglin' Fury]

Ok...so I still haven't pulled the legs of the caps but....I flipped the standby into the "play" position. No power tubes in it... on the right pair, pin 5, I now read a POSITIVE 26VDC... on the left side, where I was reading a -1.43VDC, I am now reading 429.5, yes...429.5VDC... on pin 5....something is SERIOUSLY fucked in this amp. As far as leaky tube sockets, they are ceramic and there is no carbon scoring anywhere on them. I will measure and see if it has any pins shorted to each other

[Helmholtz]

Where did you ground your black meter lead?

[Danglin' Fury]

I grounded it to the chassis.

[The Dude]

Ok...so I still haven't pulled the legs of the caps but....

The most likely cause is a leaky coupling cap, so please lift one leg of the caps out of circuit and recheck bias voltage.

[Helmholtz]

The most likely cause is a leaky coupling cap, so please lift one leg of the caps out of circuit and recheck bias voltage.

See post #14, but I doubt the PI plates are at 430V. Maybe a conductive board?

[The Dude]

Yes. I saw your post. I was just reiterating your point. If tubes are removed, PI plate voltage would be high as the tube is not there to conduct.

[Helmholtz]

Yes. I saw your post. I was just reiterating your point. If tubes are removed, PI plate voltage would be high as the tube is not there to conduct.

You're right - I didn't assume the PI tube was removed.

[The Dude]

Well, I'm not sure either. Just a SWAG (Scientific Wild Ass Guess).