An experiment for gassy tubes

[6267]

I'm sure that like me, you may have a couple of old gassy 6V6s or other tubes that you can't use since they'll run away pretty fast. I had two tung-sols (beautiful looking tubes! much cooler than the RCAs) and some RCAs that were all pulls from junk equipment. They glowed bright blue, and redplated after a few minutes.

I read that CRTs would often have their getter reflashed to rejuvenate the vaccuum. Further, I also read that during factory burn in, intentional arcing was produced in the tube since the arc somehow interacts with the gas in the tube to help either fix it to the getter or break chemical bonds in the gas or something.

Soo, with nothing to lose (free, already dead tubes) I tried RF heating the getters in the ole microwave. I think I found something on the old RAT lists that inspired me, or maybe it was a HAM site, I can't remember (I am well aware that both of these sources are sometimes crazy ).

The procedure goes like this:
1) with nothing in microwave, turn on for 1-5 seconds, until the magnetron can be heard firing...each microwave is different, mine took about 2 seconds after the light & "fan" came on before it would fire.
2) Place gassy, throw-away tube in microwave, making sure no part of the tube is contacting the metal microwave chassis.
3) Microwave tube for about 1 second (not too long!) after the magnetron activates
4) Observe literal flash of the getter
5) Remove tube and test

My results were
Tung Sol #1: Still gassy, not as bad, doesn't redplate anymore
Tung Sol #2: Still gassy, redplates
RCA #1: Perfect!
RCA #2: Less gassy, no redplate.

This is clearly a longshot, but hey, one out of four is good if you had none to start!
Any thoughts? Is this insane? Anyone tried it before?

[stingray_65]

I only thought that worked with cats
go figgure

[tubeswell]

I'm into a bit of mad science now and again - I must give that a go. Thanks for the handy hint.

[NorCalTuna]

best evar

this is the greatest posting ever made on this site. Youtube vids plz!

[6267]

The disclaimer is that it whatever you do with your microwave and your tubes is between the three of you .

Does make a cool flash, no video camera so no youtube yet. I'm interested in hearing if anyone is successful...I ran the Tung-Sols a couple times to see if I could get them to improve. The RCA was night and day.

I'm trying to remember, there's some other trick for burning cathode material off the grid of old tubes, I read it and promptly forgot.

[Prairie Dawg]

The disclaimer is that it whatever you do with your microwave and your tubes is between the three of you .

Does make a cool flash, no video camera so no youtube yet. I'm interested in hearing if anyone is successful...I ran the Tung-Sols a couple times to see if I could get them to improve. The RCA was night and day.

I'm trying to remember, there's some other trick for burning cathode material off the grid of old tubes, I read it and promptly forgot.

The old radio men used to 'rejuvenate' tubes from time to time. Sibley has a procedure in "Tube Lore" which you can read up on. I've tried it. It consists of running the tube at 2x filament voltage for about thirty seconds and then letting it cool down.
Sometimes it works, sometimes it doesn't, but if the tube's beat anyway who cares? I saved some kinda tired Bugle Boys this way one time.

[6267]

I've read about that, it's common with CRTs and it was very common with early audio tubes, apparently. Certainly worth a try! I can't seem to find the source, but there's some trick for burning the cathode material that gets attached to the grids off and reducing grid leakage/current. I think it was a charged capacitor or a slight positive voltage, but I'm not sure and I still can't remember where I read that.

[stokes]

Okay,so lets say you can burn the cathode material off the grid,how do you get it back onto the cathode it came off in the first place?Once the cathode is stripped,it is useless,so I dont see how "cleaning the grid" will improve anything.Sounds like a lot of "voodoo" to me.

[Don Moose]

Okay,so lets say you can burn the cathode material off the grid,how do you get it back onto the cathode it came off in the first place?Once the cathode is stripped,it is useless,so I dont see how "cleaning the grid" will improve anything.Sounds like a lot of "voodoo" to me.

Reverse plate and cathode voltages to reverse the flow?

[Don Moose]

Okay,so lets say you can burn the cathode material off the grid,how do you get it back onto the cathode it came off in the first place?Once the cathode is stripped,it is useless,so I dont see how "cleaning the grid" will improve anything.Sounds like a lot of "voodoo" to me.

Reverse plate and cathode voltages to reverse the flow?

- you know how sometimes I claim to have half an idea? This would be a bit less than that.

[Prairie Dawg]

Here's what I found in Ludwell Sibley's book Tube Lore.

"Rejuvenating tubes was a well known practice in the 1920s but not common later. There are 3 techniques involved. For pure tungsten filaments the goal is to evaporate contaminants by operating the tube at 100 per cent of rated filament voltage for 1/2 hour and then retest. For thoriated tungsten filaments the idea is to restore the trace of thorium on the filament surface by operating at 135 per cent voltage for 30 minutes which makes fresh thorium diffuse to the surface. Test and repeat once if necessary. If that doesn't work, take a deep breath and operate at 350 per cent of rated voltage for 30 seconds, which usually wipes out whatever emission there was. Then let the tube idle at normal voltafe for several hours and the emission may return to normal.....for cathode type filaments, direct action in nothing to lose cases is to go to triple voltage for 30 seconds, let the tube cool, and retest. One or two cycles of this treatment will improve or impair a lot of even modern tubes. Eye tubes cannot be repaired."

[tubeswell]

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.

Good to hear about that other tube rejuvenation stuff.

[Prairie Dawg]

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.

Good to hear about that other tube rejuvenation stuff.

Well, that wouldn't have worked because a white getter means you've lost your vacuum. I did try some of Sibley's tricks on some really dead Bugle Boys and it did make a couple of them usable. I think for a time in the brown amp era Fender was using Bugle Boys-woulda been mid 1960 because my brown Concert had them, and my brown Pro has them.

Anyway to make a long story short it was worth a try because they were headed for the trash otherwise. It brought the gM up to usable from beat to death.

I've also used this gambit on 45s that were pretty weak, but then I found out that it's a good idea to monitor filament voltage when testing a tube that has a heavy draw. In this case the 2.5v was being dragged way down under load to 1.8, so setting the filament voltage selector on 3v and monitoring voltage from an adjacent socket got me 2.5v under load and I found out that I was rejecting a lot fewer tubes. Same holds true for rectifier tubes as well.

Remember that you don't want a global increase in voltages (just filament) so stay away from the line adjust.

You shoulda seen the filament on the bugle boys at 18 volts....jeez...like a light bulb.

[ThermionicScott]

Success!

I just tried this trick on an old Sovtek 5881/6L6WGC. In my 5E7 clone, it tended to "eat" a couple volts of bias, and glow a dull red as it gobbled up extra current. Thankfully, it always stabilized itself at that point, and never went past 25W or so.

So I saw this thread and had to try it. I upended the tube on top of an upside-down tumbler to position the getter at the center of the microwave. (Those flat-topped Sovtek tubes make this easy!) On my first attempt, I saw the heaters glow at the base, chickened out, and retested the tube in my Seco 107, fearing that I'd destroyed it. Whew, it was fine, so I tried it again.

This time I managed to wait until there was another white flash at the top of the tube before hitting the Stop button. When I pulled the tube out, I noticed some crazing patterns in the inside of the getter. It tested fine, so I threw it back in my amp.

I was horrified to see a bright blue haze fill the tube. Thankfully, it abated -- must have been the liberated gases being eaten by the getter. After a few minutes, I was pleased to see that the blue glow was mostly gone, and the plate wasn't glowing at all!

Time to raise the stakes. I powered down the amp, replaced the 5U4GB with my Sovtek 5AR4, and turned it on again. In my amp, this raises the B+ by about 25 volts, and generally exacerbates the tube's tendency to runaway. After letting the amp "cook" for about half an hour, I'm happy to report that not only is the tube behaving as well as its partner, its current draw is now within 2mA of the other!

Gotta love those hams for thinking outside the box.

- Scott

[Prairie Dawg]

I just tried this trick on an old Sovtek 5881/6L6WGC. In my 5E7 clone, it tended to "eat" a couple volts of bias, and glow a dull red as it gobbled up extra current. Thankfully, it always stabilized itself at that point, and never went past 25W or so.

So I saw this thread and had to try it. I upended the tube on top of an upside-down tumbler to position the getter at the center of the microwave. (Those flat-topped Sovtek tubes make this easy!) On my first attempt, I saw the heaters glow at the base, chickened out, and retested the tube in my Seco 107, fearing that I'd destroyed it. Whew, it was fine, so I tried it again.

This time I managed to wait until there was another white flash at the top of the tube before hitting the Stop button. When I pulled the tube out, I noticed some crazing patterns in the inside of the getter. It tested fine, so I threw it back in my amp.

I was horrified to see a bright blue haze fill the tube. Thankfully, it abated -- must have been the liberated gases being eaten by the getter. After a few minutes, I was pleased to see that the blue glow was mostly gone, and the plate wasn't glowing at all!

Time to raise the stakes. I powered down the amp, replaced the 5U4GB with my Sovtek 5AR4, and turned it on again. In my amp, this raises the B+ by about 25 volts, and generally exacerbates the tube's tendency to runaway. After letting the amp "cook" for about half an hour, I'm happy to report that not only is the tube behaving as well as its partner, its current draw is now within 2mA of the other!

Gotta love those hams for thinking outside the box.

- Scott

A lot of the really creative ideas came from radio repairmen during WW2 when replacement tubes were made of unobtainium. Later on there was a limited release of certain tube part numbers but they were still hard to get.

I've been re-reading Tyne's "Saga of the Vacuum Tube" and it makes for interesting reading. Back in the day a number of tubes were made with dual filaments in case of burnouts, and then some people repaired tubes. I think that this was fairly common practice with transmitter tubes.