HELP!!! with tube please

[eschertron]

Thank you for understanding what I'm trying to achieve, so my question would be to you if one of those caps would be leaking could that cause my total resistance in that circuit to show weak it reads at 20 ohms less than it should , the 47k's in the series are reading within 1 ohm, wouldn't this cause voltage to go up closer to transformer output rather than drop?

The resistors are listed as being 5% tolerance parts, so the reading you got are consistent (mostly consistent) with the schem.

If c32 or 35 were both leaking would this lower voltage?

The tricky part is figuring out why you got readings that differed the way they did. Coupling caps aren't likely failure points, as far as I know. If the results you got are consistent and repeatable, then maybe the experimental design is flawed because there's another factor we haven't considered. Dirty sockets? I don't know. If the amp looks good, and smells good, then I think it's time to swap out the tube. So my suggestion is to see if replacing the bad tube clears up the problem. Tubes go bad. That's why they're in sockets

[DRH1958]

"Quote: Another example is the Fender Hot Rod DeVilles, 30mA per tube for 6L6s. "

That's not cold.

Well, I suppose it depends on what your definition of cold is. Plate voltage on those is 485v. 485 X .03= 14.55 watts. This is less than 50%. I would call that cold. Maybe you wouldn't.

[g1]

Initially the fault followed the tube when you moved it. So it's not a socket or solder issue.
My question is why you don't have -14V at all pin2's when all power tubes are removed. With them removed, it is open circuit so there should not be any voltage drops.

[eschertron]

Initially the fault followed the tube when you moved it. So it's not a socket or solder issue.
My question is why you don't have -14V at all pin2's when all power tubes are removed. With them removed, it is open circuit so there should not be any voltage drops.

Right. I agree it is perplexing. But because we notice phenomenon A at the same time we notice phenomenon B doesn't mean they're related. I take the blame for being the first to suggest there might even be a component other than the tube that is bad. My apologies. I'd like to see the initial problem addressed first.

[DRH1958]

Absolutely agree g1 but at these plate and screen voltages(332,328), -11 v will keep the tubes from redplating, especially since only one did this. OP has a point about leaky caps. How else can the -14v turn into -11v? With tubes out, the only other components hooked up to this point are those coupling caps, C32,35. I would suspect C35 because it is hooked to ground through R54. If this is leaky, this is where you would lose voltage. Try a new tube to replace the one that redplated and see what happens. The tube is probably bad and this is the source of the hum. In his second pic in post #25, the redplating is gone but still has hum. If the hum disappears, replace with matched tube or get a new quad and now you have spares. Then with voltage applied with tubes in, get a reading at the grid side of those coupling caps for DC, especially C35.

[Enzo]

If C35 were causing this redplating it would happen in BOTH V6 and V7. And remember with this split load phase inverter, that cap is not connected to ground through R54, R54 will have something like +50v on it. That doesn't mean don't check it, just a thought experiment.

What could haul -14 down to -11v? Any number of things. If a tube grid was a dead short to ground, then the voltage divider thus formed by the 47k, 220k, and the 47k in the bias supply would drop 14 to just about 11. And you'd red plate that shorted tube. But also if the -36v is down to about -30, that too would explain it. Then any shift in the values of R63, R64 could do it. The -36 is used for the 12AX7 heaters. If a tube had a heater to cathode short, that could load down the -36, and thus the -14. And might also cause hum. A super leaky C44. Seems unlikely, but possible. For that matter a leaky C46 on the -36 could cause the -36 to drop nd so the -14, and cause hum as well.

[g1]

Just wanted to make sure a potential bias issue does not harm any more or new tubes. The question was asked if something could have caused the fault. Running too hot bias could have led to premature failure of this one power tube.
Best to solve any bias questions with the power tubes removed. Partial loss of bias voltage in an open circuit just doesn't seem right.
Coupling caps suggested by DRH are good suspects, disconnect one end each of C32 & C35, then see if you get -14V at pin2 of all power tubes.

[g1]

Enzo, the -14 is there, but dropping to -11 at the sockets with power tubes removed.