An experiment for gassy tubes

[ThermionicScott]

I've zapped a couple more tubes and gotten mixed results.

One was a tired 5Y3GT from a Muzak PA. The getter flash is dark-brownish, so I figure it wasn't long for this world anyway. It tested at about 50-60% on my Eico 701, and put out roughly 10V less than my other 5Y3s. After zapping it for a few seconds, it pegs the needle of my tester, just like the healthy ones! I guess the microwaving can not only flash the getter, but possibly (re)activate the cathode as well.

The other tube was a tired GE 6V6GT, from the same PA. It tested around 60%, and would fall off when holding down the lever on the tester. I zapped it long enough to see flashing but I must've gone too long, as I've lost filament continuity.

Just a couple more data points for you folks...

- Scott

[Bruce / Mission Amps]

I've zapped a couple more tubes and gotten mixed results.

One was a tired 5Y3GT from a Muzak PA. The getter flash is dark-brownish, so I figure it wasn't long for this world anyway. It tested at about 50-60% on my Eico 701, and put out roughly 10V less than my other 5Y3s. After zapping it for a few seconds, it pegs the needle of my tester, just like the healthy ones! I guess the microwaving can not only flash the getter, but possibly (re)activate the cathode as well.

The other tube was a tired GE 6V6GT, from the same PA. It tested around 60%, and would fall off when holding down the lever on the tester. I zapped it long enough to see flashing but I must've gone too long, as I've lost filament continuity.

Just a couple more data points for you folks...

- Scott

OK ... since I have dozens and dozens of these old used rectifier tubes, I tried this with three old American made used 5Y3GT tubes to see what would happen.
On the Hickok #533's English scale, they all were testing just under what a well worn tube would, but they all still worked, just not in the green "good" part.
I put them one at a time in microwave oven for a just a couple-few seconds each and then I ran them over to the tube tester...
One did get better, much to my disbelief, in the green and I was encouraged, but the next one quit working completely and the final one.... well, the damn the glass broke open in the microwave. Spfft.
I'll try again and report back... but right now, I'm having a hard time buying into it, yet one did get better and I know how to work my test equipment.

[Sweetfinger]

Well I tried the microwave trick a while back with a NOS 5Y3GT that had all this powdery white stuff on the inside of the tube beside the getter, but alas it didn't bring that tube back to life.

White powdery stuff means the tube has lost vacuum. No microwave's gonna fix that!

[stingray_65]

Ok,
What seperates a "gassy" tube from just a old wore out tube?

[tubeswell]

White powdery stuff means the tube has lost vacuum. No microwave's gonna fix that!

Yep thanks Sweetfinger, Praire Dawg confirmed that (last May - see above)

[Sweetfinger]

Yep thanks Sweetfinger, Praire Dawg confirmed that (last May - see above)

Y' know, ..I don't seem to have a good excuse for my redundant post. I'll swear I didn't see the earlier info- sometimes I don't see all the posts in a thread and have to click on "more replies below current depth" in the thread window- even if I've clicked "last page". This seems to be a relatively recent development in display modes- 1 or 2 years?
This quirk got me real twitchy the first time I encountered it. I kept trying to get to MY post in a thread but it wouldn't come up no matter how I switched display modes. Anybody got a fix?

[ThermionicScott]

This quirk got me real twitchy the first time I encountered it. I kept trying to get to MY post in a thread but it wouldn't come up no matter how I switched display modes. Anybody got a fix?

Yeah, switch to "linear" mode under the "Display Modes" pull-down menu. Thread modes where you have to click on each post to read it belong in the past.

For stingray, a gassy tube will have excessive grid current flowing at idle. Positively-charged gas ions are attracted to the grid (the most negatively-charged item in the tube), and each collision makes the grid a little more positive. This causes the tube to draw more current, ionize more gas molecules, and reduce the bias even more, leading to a "runaway" condition in some tubes. Like the ones in 6267's post that would redplate in a short amount of time.

Excessive gas in a tube wears out the cathode coating, so while a gassy tube may test as weak, a weak tube might not necessarily be gassy.

- Scott

[Bruce / Mission Amps]

Well, I have know killed at least 9 old GE, RCA and Sylv 12AX7s, 12AY7s, 12AT7s and a small handful of really poor 5Y3GTs, 5U4Gs and Bs and a soggy Russian GZ34.... all with less then 2 second bursts from my 1Kw micro wave... I'm afraid this story is really weak and getting weaker.
Flash to trash.