Need some help on an 8TS30....

[Kamakiri]

Geeze louise....I gotta work for a living too, y'know! So nyah

Since one end of the resistor's already disconnected, that made it easy. 234 ohms. I knew it would be because I replaced it earlier, unless it fried, which it didn't.

I'll do some wire tracing when I finish work for the day......

[Kevin Kuehn]

Sollder that puppy back up and lets get a voltage measurement acrost it. Plus it would be cool if you could make a video of solder melting off it's terminals.

[Kamakiri]

What range should it read? In an earlier post, earlyfilm was mentioning a slow power up, but I can't hit those low voltages with my variac. The lowest it will go is 75 VAC.

I'll keep my digital camera handy for your amusement should it reoccur

[old_coot88]

Since you've replaced R127B with a chassis mount type, and verified its resistance, what is the actual wattage rating of the replacement?

[Kevin Kuehn]

Originally Posted by Kamakiri

What range should it read?

Based on Riders voltages I'm coming up with 39.4v across R127B, which would be about 6.77 watts. Or 57.4v from the left side terminal to ground. 9.84 watts dissipated between those three series resistors. Then another 9.323 watts across R127A and R128A. For a grand total of 19.16 watts in the chimney. Does that sound feasible?

[old_coot88]

So based on 40V max across R127B, it should be rated at at least 10W, preferably higher (I'd prefer much higher for cooler running).

[Kevin Kuehn]

Originally Posted by old_coot88

So based on 40V max across R127B, it should be rated at at least 10W, preferably higher (I'd prefer much higher for cooler running).

Sams lists it as a 10 watt. 17 watt for R127A. They're really banking on that chimney to draw cool air in.

[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.

[Kamakiri]

Originally Posted by Kevin Kuehn

Based on Riders voltages I'm coming up with 39.4v across R127B, which would be about 6.77 watts.

I'm at 45.8v across R127B, running the set at 117 VAC.

[old_coot88]

Originally Posted by Kamakiri

I'm at 45.8v across R127B, running the set at 117 VAC.

Kinda high. The current will be 196 ma. @8.96 watts. A 10W resistor will run sizzling hot.
196 ma. is the total current of the entire B supply going thru that resistor
What does the voltage across it drop to when you pull the 6BG6?

(Edit)
In a darkened room, does the 6BG6 show any sign of red plating?

[Kamakiri]

R127B I have a 10 watt, R127A is a 20 watt. R127B is a chassis mount, but since the arcing issue a couple pages back, it's just floating loose in space at the moment.

[old_coot88]

So what's the actual DC voltage you have across R127B (at normal line voltage or whatever voltage you normally run the variac at)?

[Kamakiri]

With the 6BG6 pulled, I'm at 48.9 VDC. Can't see any hot plating.....

[old_coot88]

Originally Posted by Kamakiri

With the 6BG6 pulled, I'm at 48.9 VDC. Can't see any hot plating.....

Holy makrel! That's over 10 watts. Try pulling the damper, and then the rest of the tubes one at a time, starting with the audio output, while watching the voltage across R127B. If the voltage stays up, it'll prove there's not a tube overconducting.

To save brutalizing R127B while troubleshooting, you could sub it with a couple of 100 ohm 10 watt resistors in series if you happen to have such.

[Kamakiri]

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?

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.