Need some help on an 8TS30....

[Kamakiri]

With both the 5V4 and the 6BG6 removed, it dropped to 44.9 VDC. Continue pulling tubes and checking, or stop here?

[Kevin Kuehn]

Any chance you could show us a picture of the inside chimney wiring? Another very strange thing, is how you mentioned earlier that R127B was arcing to ground. There shouldn't be any voltage potential on that resistor high enough to arc to ground, unless you meant one of it's terminals was touching ground. Is R127B an aluminum cased or ceramic coated?

What's the voltage reading from either side of R127B to ground?

[Kamakiri]

Bear in mind that this isn't the "finished product", as I'm moving things around, testing, etc. My finished work is much neater.

R127B is on the right, that's the gold chassis mount resistor. R127A is the enameled wirewound. You can see how the previous R127B just let loose. It wasn't touching ground, it had an arc jump TO ground on the right side. It was close to ground, but not touching. Probably 1/8" or so.

[Kevin Kuehn]

It's hard for me to see clearly what's connected to where, but is that a 10 ohm cement coated Dale, with the left end connected to chassis ground? And where is the other end of that same resistor going? Edit- I guess that 10 ohm Dale is in series with the 12 ohm(128B)?

[old_coot88]

Deleted. Posted too soon

[Kevin Kuehn]

If my eyes are not deceiving me, and that is a 10 ohm cement Dale resistor that's replacing the 6750 ohm candohm section, then there's one heck of a load on the B+. But I'm having a hard time seeing the connections.

[old_coot88]

At this point, with the chassis still in fault mode, I would put an ohmmeter on the main B+ rail, to ground. A good place to find the B+ rail is the width coil or the top of filter caps C3A/C2B. (with the set off, of course.) Connect the positive lead to the B+ rail, negative lead to ground. What reading does it settle into after the initial charge-up spike?
Does it stop hard at a few K ohms, or drift up into the fractional-megohm range?

[Kamakiri]

Originally Posted by old_coot88

At this point, with the chassis still in fault mode, I would put an ohmmeter on the main B+ rail, to ground. A good place to find the B+ rail is the width coil or the top of filter caps C3A/C2B. (with the set off, of course.) Connect the positive lead to the B+ rail, negative lead to ground. What reading does it settle into after the initial charge-up spike?
Does it stop hard at a few K ohms, or drift up into the fractional-megohm range?

Voltage test didn't change with all 4 tubes removed, so I went on to this. The meter stopped at almost exactly 6.8 K Ohms.

[old_coot88]

Originally Posted by Kamakiri

Voltage test didn't change with all 4 tubes removed, so I went on to this. The meter stopped at almost exactly 6.8 K Ohms.

Well, 6.8K is reasonable enough, considering that the B+ bleeder string to ground (R127A and R128A) add up to 8.1K. Current will only be around 45 ma., nowhere near the 175 or so ma. that's going thru poor R127B.

It almost looks like a B+ filter cap is breaking down under voltage, like maybe a cap has been replaced with one having too low a voltage rating. The most likely suspect would be C4A, which should be 40 mf and rated at 450V. Does the C4 can show evidence of heating?

[Kevin Kuehn]

Any progress on this?

I'm curious how much your B+ increased when you pulled those 4 tubes? Or if it didn't, I'd continue to pull tubes, one at a time, except leave the audio output tube in. Continue to check voltage across R127B and B+. Make sure B+ doesn't exceed your 450v cap ratings while doing this.

[Kamakiri]

Originally Posted by old_coot88

It almost looks like a B+ filter cap is breaking down under voltage, like maybe a cap has been replaced with one having too low a voltage rating. The most likely suspect would be C4A, which should be 40 mf and rated at 450V. Does the C4 can show evidence of heating?

C4's been replaced with all new Nichicons. C4A is now 47 uF @ 450v. Don't see any signs of anything under there.....