I found this 6X5GT in a box of old tubes that I have had for a long time. I decided to not even test it because it appears that there was arcing from plate to plate. Is that normal or was there some kind of fault causing this? Also, where did the bottom plate arc to? Or, do I have it all wrong. I hear a lot about 6X5 tubes. This one has already been tossed into the bin.

Also, is this the plate design that is not to be trusted? I do have some 6X5GT tubes that are constructed differently.

Thanks!

6X5's can arc from plate to plate as well as from plate to cathode. That's why you have to fuse the plate circuit if you want absolute protection, which Zenith actually recommended in their sets that were experiencing catastrophic failures.

Yes, that is one of the styles most likely to fail. The last version made which had an "X" configuration for the plates is the best.

Is this the better plate structure that we should be looking for?

Yes, that is a good one. Looks to be a 6X5WGT.

Thanks, that is what it is labeled (not mine but I have some like it).

If you did not test the tube, then it’s only speculation that the tube is shorted.

In that design, the two plate assemblies are stacked one above the other. Plate to plate shorts are extremely unlikely unless the mica separator breaks down. Takes a warranty-voiding amount of voltage to do that. Plate to cathode shorts are still possible, though you usually only see them on one plate or the other since Zenith power transformers were designed to burn out and protect the other plate.

The tube clearly red-plated for a long time and at this point I wouldn’t trust it any further than I could throw a grand piano. But I’d bet the damage was caused by a short in whatever equipment it was used in.

Greetings to the Forum:

I agree with Chris... that damage is over-current damage, probably not plate-to-place arcing.

Regards,

Thanks for all of the replies. While I didn't even test this tube, I would have thrown it into the bin had it tested good. I have enough other tubes that I didn't need this one. Just interesting how it looked.

I looked at the schematic and it shows that -500 volts was on the plates and they were were tied together. Interesting.

Again, thanks.

More plate damage there than a three stooges episode. Craig

Good one, Craig. How's it going out there?

Today, I was emptying the rubbish can in my office and I found this tube! I thought that it and been tossed over a week ago. I tested it and it shows no shorts, no leakage and excellent emission. Now what!

Looking at the plates, they are not warped. Rather, it appears to me to have arced, not overheated. According to the schematic, there was ~ -500 VDC to ground on the plates. The tube was in a scope.

I guess the consensus is that there was an arc over as opposed to an overload?

Sorry, not trying to beat a dead horse here.

I'm sticking with red-plating due to a short in the equipment it was used in. The parts that are melted are the thin areas where the halves of each plate assembly were crimped together. That's where the metal is thinnest and most likely to start melting. The top and bottom edges of the plates which are adjacent to each other don't show any signs of damage, and that's where it would arc if it was going to.

So it's not shorted and has good emission, but I certainly would rather toss it at the parkway bridge than have to replace a power transformer. If it has been egregiously overheated as I suspect, the plates and separators could be loose and that may lead to shorts developing if you were to use it in a piece of equipment.

Absolutely...

Maybe something to "display"...

You could start a display of defective and abused tubes!

I was thinking of starting a gallery of exploded tubular capacitors here in the “Tubes and Parts” category.

EB