Need some help on an 8TS30....

[Kamakiri]

Originally Posted by Kevin Kuehn

Is it possible the other green wire you have going to the left end terminal of the Candohm, is also grounded, and that should be on the right end of the 6750 ohm section? It would make some sense that those two green wires disappear to a ground lug under the chassis. Sorry about so many details, but it's just a little confusing in that chimney.

Hah, you're tellin' me!

No, in effect for some reason (read brain fart) I didn't realize at a glance that the funky cloth covered little inchworm was a 12 watt resistor, so I added a 10 watt resistor where it should have gone according to the Sams, thereby giving that part of the circuit a 22 ohm resistance instead of 12.

Then, that 6750 ohm section should have had the inner terminal going to chassis ground, and I believe I just got confused working from the schematic alone.

I'll order up some parts tonight, and double check them against another 8TS30 I have here.

[Kevin Kuehn]

I found this picture from another thread here. Looks like what I thought were green wires are not suppose to be grounds. Apparently the ground connections are to be soldered directly to the chassis below the chimney, as shown. Sorry for making things more confusing, I've never restored one of these RCA sets.

[Kevin Kuehn]

Originally Posted by Kamakiri

Hah, you're tellin' me!

No, in effect for some reason (read brain fart) I didn't realize at a glance that the funky cloth covered little inchworm was a 12 watt resistor, so I added a 10 watt resistor where it should have gone according to the Sams, thereby giving that part of the circuit a 22 ohm resistance instead of 12.

Then, that 6750 ohm section should have had the inner terminal going to chassis ground, and I believe I just got confused working from the schematic alone.

I'll order up some parts tonight, and double check them against another 8TS30 I have here.

OK, you posted while I was out looking for another reference photo. Sounds like you've now got your head screwed back on straight.

[Kamakiri]

And I should really know better, too. This is the 2nd 8TS30 I've done, and before that I've got a Crosley 630 clone, a DeWald BT-100, and an RCA 9T246 under my belt.

I think I tried really hard to forget about those spiders nests as soon as I finished the job

There's one more unrestored 8TS30 sitting here staring at me too

[Electronic M]

If it is still acting up once you rewire it, check the candohm for shorts to chassis.

[Kevin Kuehn]

Originally Posted by Kamakiri

And I should really know better, too. This is the 2nd 8TS30 I've done, and before that I've got a Crosley 630 clone, a DeWald BT-100, and an RCA 9T246 under my belt.

I think I tried really hard to forget about those spiders nests as soon as I finished the job

There's one more unrestored 8TS30 sitting here staring at me too

Sounds like too many caps ago, and too little time.

[Kamakiri]

You're not kiddin'.....

There's got to be a 6.8K ohm resistor around here somewhere. Time to go dig through my wirewounds.

[Kamakiri]

Okay, something's still very wrong. Here's where I'm at.....

I found a 7K ohm 10 watt in my stock. Close enough to give it a try. I'm getting 39.8 V across R127B, so we're right there in the correct range. Now, the horizontal linearity is WAY off, compressed on the left side (as I recall).

But everything's getting hot still. Really hot...to the point where something was starting to give a wisp of smoke. When I lifted the leads off R127B after the set was shut down for a couple minutes they were still extremely warm. The contrast/AGC control does almost nothing now, and the picture has slightly less width than it had.

Here's my work as it is now. The 12 ohm resistor to chassis ground checks out fine.

[old_coot88]

OK, now try the same power-up except with the 6BG6, damper, vert.output, and audio output tube removed, while monitoring voltage across R127B. It should drop 'waay down with those heavy-draw tubes removed.
If it doesn't, try the ohmmeter test suggested in post# 75.

[Kamakiri]

I'll pick it up here tomorrow. Gotta go work the night shift on the railroad tonight

[Electronic M]

Originally Posted by Kamakiri

I'll pick it up here tomorrow. Gotta go work the night shift on the railroad tonight

Good ol' Lionel "O" scale model RR...Used to set up my father or grandfather's set 'round the tree most Christmases....The tracks liked to push apart when the train went over it and speed dropped a lot on the far side from the power connection to the tracks.....Until I tried tying the track sections together, then they did not come apart and power loss along the tracks dropped significantly.

[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]

Good timing, I just pulled the chassis back out a couple minutes ago. Christmas stuff's delayed my work a bit.....stand by.