Need some help on an 8TS30....

[Electronic M]

Captain, if your sick of this one and nothing prevents either of us from going to the meet I'd be willing to take it off your hands....especially if it is the one with the blue tinted screen (that thing is wicked awesome looking).

[Kamakiri]

It's R127B again, but R127A's getting pretty toasty too. And no, it's not the one with the blue screen....although I've been thinking of selling that one, actually . This one belongs to Rodmonster, I'm doing him a gigantic favor.....

No, no, I didn't get sick of the set....we just had a rare couple of 60 degree December days in Buffalo, so I wanted to take full advantage of it to get some work done on the TV hauler.

This is the picture I got on the screen just before the "meltdown". The resistor itself looks okay, admittedly I didn't ohm it out yet. The raster is full width, but the picture is not.

[old_coot88]

Originally Posted by Kamakiri

It's R127B again, but R127A's getting pretty toasty too.
....... The resistor itself looks okay, admittedly I didn't ohm it out yet.

OK lessee if I got this right now.
R127B corresponds to Riders R185A (the right-hand section of the big honkin' chimneyed resistor shown in post# 26). If so, it should measure 230 ohms with one end disconnected.
If it's signifigantly higher than 230 ohms, it would definitely overheat as well as drop the main B+ a bit.
----
Is there any chance the replacement was swapped end-for-end when installed? If so, it would explain the overheating since the other section is 1360 ohms. (it would probably explain the width anomaly too)

[Kamakiri]

About a 99% chance that's not the case. When I started having issues that prompted this thread, I checked the wiring against two other 8TS30s, one unrestored and one I restored about a year ago. Both were a match.

[old_coot88]

So.. have you physically disconnected one end of R127B and ohmed it for 230 ohms? And verified that circuit-wise it's connected correctly (i.e., one end going to the ion trap and the other end to the 93 ohm resistor R128C)?

[Kevin Kuehn]

Originally Posted by old_coot88

OK lessee if I got this right now.
R127B corresponds to Riders R185A (the right-hand section of the big honkin' chimneyed resistor shown in post# 26). If so, it should measure 230 ohms with one end disconnected.

You got it. Now if we could only get our field representative to take a couple measurements...

[old_coot88]

Sotta like gettin' Hannibal over the Alps.
Just Kidding!!!!

[Kevin Kuehn]

I'm glad YOU said that.

[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.