Getters

[KE6DF]

I have some large old transmitter tubes from the 1930's era.

Some have large shiny sliver colored getters. I figure those are probably good, or at least they have maintained their vacuum. (emission of the filaments might be down, of course)

I have other tubes where the getter has turned white and chalky and I assume those probably have leaked and are like not usable.

But there is a third category where the getter is almost clear, but has a rainbow like edge. Not white, but clear.

Is this third category of clear getters likely bad tubes?

Or is it a different kind of getter-ing material?

I'm talking big tubes like 810's, 828's, 805's, and 211's

Dave

[K6IC]

Hi Dave,

Certainly,  tubes with white/flakey/chaulky getters have leaked air inside.

Some glass tubes do not use the silvery getters,  but use a metallic coating ON the plate.  These use normal heating from power dissipation heating the plate,  to scrub the vacuum.

I've noticed that some 833A's (Chineese ones with cast, or extruded plates) have the Getter structure,  but these getters have not been finished (by induction heating).  These tubes must use the coated plate for gettering.

It is possible that some of the tubes with little silvering use a plate coating,  altho,  this coating may not have been used in the 40's era tubes,  altho in the 50's Eimac and others commonly used coated plates.

W8JI has some interesting info on gettering :

http://www.w8ji.com/vacuum_tubes_and_vaccum_tube_failures.htm

73  C U on  AM.   Vic

[W7TFO]

I have a number of the the tube types you mention, and with that comes a plethora of getter signatures.  Some have shiny, some have rainbows, some have none at all yet there is a getter ring.  White getter flashes are obviously pointing to a NG tube.  Eimac and H-K usually don't have getters as the innards are mostly Tantalum and supposedly free of trapped gas, but leaky seals or whatever cause them to get a bit on some samples.

I test large tubes in my HB emission jig (Pardon the dust), and I don't keep any that are not up to par.  I used to trash a lot of gassy tubes, but now things have changed;

The big problem is that inherent gas, and I use a technique pioneered by Machlett Labs back in the 50's that successfully kills the gas and so am able to use the tubes again about 80% of the time.

One puts the tube in a circuit of high voltage AC, up to 15kV.  A neon tube transformer on a Variac does the trick.  No filament emission is used here.

Connect all filament pins to one pole, the plate to the other.  Advance the E up to the point where the gas will ionize, and let it burn for a while.  Run the E higher until it dissipates the glow if possible.  Back it off if there is interelectrode arcing. 

I'd only do this with tubes that have plate caps, or at least jumbo bases like the 203A.

The tube is acting as a glow-discharge device at this time, and with no emission most of the gas is transformed to a harmless deionized state that will not conduct.

At times I have seen the getters change color after this treatment.  What do you have to lose, anyway?

dg

[WBear2GCR]

WHOA!

This is interesting!

Anyone else try this method with any sucess??
I have everything necessary to do the job!! 

And some gassy 4-400s to test upon!!

It is unclear how or why the AC would have any effect beyond ionizing the gas, and I'd love to know the theory behind it too...

...and why AC and not DC?

I wonder if it will work on smaller tubes using a solid state current limited HV supply?? I have several of them around, commonly used in various applications some years ago, Spellman High Voltage is/was one manufacturer of these supplies... thinking that the current limiting and the rather pulse like nature of the output is AC enough to ionize the gas within...

Anyone else on this??

[Ed/KB1HYS]

I believe (probably wrong, but I don't have my vacuum theory books here at work) that what is going on there is actually Ion-pumping of the tube. The HV ionizes the gas and the ions "stick" to various surfaces in the tube. I think they bind to other molecules (metal probably) where they can pick up the electrons they need to return to a normal state. DC voltage would Ionize the gas, and the ions would go to the opposite pole. Might still work but I think the gas ions would end up at one end of the sytem (tube). and possibly poison it. AC would keep the ions moving a bit (not sure what the mean free path and velocity would be) so the odds of not all hitting the same thing is better.  Most likely ions running around in the plasma in the tube would eventually hit the getter material and "stick" there. Which is what the getter is supposed to be for anyway. 

All this is strickly conjecture on my part, I'd need to do some research that I can't right now to be sure.

[W7TFO]

I'll scan the article when I get back home next week and post it.  It has some photos, and the transformer used resembles an old Thordarson spark job.

Dennis

[KM1H]

Please DO post that info. Im curious if it is applicable to both filament and cathode tubes?

Id also include a 1M limiting resistor in the HV as is used with a Hi-Pot tester. Old bug zapper and sign transformers should work well.

When finished the de-ionizing then do a Hi-Pot if the HV will be substantial, such as a modulated 4-1000A,  if there was any arcing during the process.

Carl
KM1H

[N3DRB The Derb]

Thordarson spark job

there was a 250 watt Thor Type RS spark transformer on ebay a few weeks ago. the sec.voltage on the nameplate was stamped 7500.

it looked like it was in pretty good shape - went for 150 bucks and some change.