Need some help on an 8TS30....

[old_coot88]

Originally Posted by Kamakiri

This is something I've never done before. I was always under the impression that I'd end up damaging something doing that if I yanked more than one out.

Ordinarily*, pulling tubes might allow B+ to go too high, stressing the filter caps. But in this case, there's already a huge draw on the B supply. And you have a variac to keep it under control.

Just so that I have this right, I'm gonna next pull the damper, power it up, then start powering up the chassis, each time yanking a tube and watching the meter, looking for a change in voltage?

Basically yes, using your variac to bring it up each time. Actually, just do the damper> AF out> vert.out for now.
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*One big no no would be pulling the H.osc tube while the H.out tube is still in place.

[Kevin Kuehn]

Wow, I don't understand how removing load from B+ can cause the voltage across R127B to go higher.

[earlyfilm]

First verify that your rectifiers are 5U4's and the damper is a 5V4, which is a rather unusual choice for a damper.

Yes, pull both at the same time. A shorted damper can kill a new horizontal output tube and I normally yank both together. The multiple tube pull method won't work on stacked power supplies, but the stacking is limited in this set.

If the voltage across the resistor is as high as before, immediately kill the power and feel all electrolytic caps.

Don't worry about the HV, as it wont be working, but don't touch the chassis and an electrolytic at the same time as some might have lingering B+. If one is heating, check for incorrect wiring, ratings and polarity on the hot one(s).

If no electrolytic is heating, print out the RCA Factory Schematic and Wiring diagrams from the RCA 8TS30 PDF on ETF and give them to your son and offer him a reward if he can find your wiring error starting from the Power Supply and Reaction Scanning (damper) tubes. The wiring error could be something as simple as a tube in the wrong socket . . . . . or a grounded floating ground . . . . or an electrolytic with polarity inverted.

Jas.

[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.

[Kamakiri]

Left end is to chassis ground, right end is connected to the 3rd terminal of the candohm. That section of the candohm was dead.

[Kevin Kuehn]

Something does not look right there. Am I correct that the cement Dale says 10 ohms on it? Compare your wiring to what Riders shows. I added the resistance values in red.

[Kamakiri]

No, the 10 ohm is replacing the 12 ohm R240, which was open on the candohm. But the ground is totally disconnected from the second pin of the 6750 ohm candohm section, and I relocated it to the Dale resistor rather than jumpering it across. The hell??? Before it all made sense to me, now I'm looking at this wondering what the devil I did here.....

[Kevin Kuehn]

Well what's confusing me, is that Riders only shows two resistors in that Candohm, but Sams lists sections A,B,C. Yet your picture seems to show a separate resistor for the 12 ohm?