Oh, No, Purple Glow!

[bgadow]

Another long-winded story from Bryan...last year I was given a Zenith Flash-Matic. The crt is all used up. 24 hours at 8 volts barely moved the needle. Into the corner it went. The set has a 21ALP4 and while there are a lot of subs listed in the different books, I didn't have any of them. Well, the other day I was checking out my old DuMont 21" set, about the same age, and found that the Sams lists it as using a 21ATP4, one of the subs. But when I checked it out I found the original had been replaced with a Silverama 21CBP4, not on the sub list...but I have a NOS Channel Master 21CBP4 up in the attic! If it will work for the DuMont it should work for the Zenith. Well, when I saw this I couldn't wait to make the swap. (I had been saving that tube for a Motorola I have that is watchable but weak)

So, I pulled the chassis (thats a big crt to be chassis mounted!) and did the switch, no big deal. The neck is a lot shorter on the CBP4 but it fits. (inside the crt box is a substitution guide listing this as the appropriate swap) While it was out I swapped the caps in the vertical circuit, since the set had the typical height/lin problems. I put things back together, plugged her in and threw the switch. And then...

THE PURPLE GLOW OF DEATH

Yes, that Channel Master, waiting in a box since 1969, has apparently gone gassy. I guess. I get a fantastic purple glow in the neck. So I tried the crt tester and the filament lights fine but no emission. I crank it to 8 and let it sit, when I come back the emission reads great but there is a faint purple glow. I wish the tester was better, it's pretty basic. I've manually looked for shorts and found none. I've tried running the heater off an isolated power supply, no change. I don't guess there are any other ideas out there? Yeah, I also used my handy-dandy crimping tool on the pins in case there was a bad connection. This crt being a dud isn't the end of the world, but I just don't want to toss it prematurely.

It is good to know that a CBP4 will fit here...I have a couple sets I could part out and get usable crts, if I could bring myself to do it. The DuMont, for one, would make a good donor. One last try on my "Spring Cleaning" thread, I guess. I'll have a pic on there soon.