There's a cutoff knob on the CR-70. You're supposed to turn it till the needle sits in the cutoff area, then read emission. With a gassy tube there is no getting it to sit in the cutoff region, because as soon as it reaches a certain point it will go right to full conduction and peg the needle. That's the gas regulator action I was talking about- full on or full off is all you get. Yes, my tube had a purple neck glow that s typical of gas.

This is what it looks like on a 15GP22:

http://www.earlytelevision.org/images/PURPLE-GLOW-1.jpg

It's not that glass to metal is a problem, there are NO MORE tube rebuilders in the USA. Until ETF gets their stuff up and running, we're all sitting on a pile of useless tubes.

Yes, that's the 'Light-show' all right. I only noticed it after clearing flyback problem from chassis (after recapping) which restored B/Boost, Focus, HV -- but didn't see this glowing with CRT tester.

This CRT won't even achieve "cutoff" set up (on B&K tester) or "Gun Balance" (on Sencore tester) so no chance of emission - tho I didn't crank up filament beyond 6.3v(taking it easy considering gun assembly may be suitable to be reused in rebuild).

Now that chassis is done , will look at using a 21" Rauland or Zenith glass tubes that I have (not fully original I know) and store the AXP in hope of future plant operation.

There'll be a lot of business waiting for an operational CRT plant.

Once they’ve done a few dozen (?) of catch up tubes, they'll likely be setting there wondering where the next paycheck is coming from. At least that's my opinion of the situation. It's going to take one very charitable individual to do this as a service to us TV restoration hobbyists.

Kevin

I don't remember local rebuilders offering re-built 21AXP22's. They said the mortality rate was too high. They didn't even like doing metal B&W CRT's.

Now here's a GP22 I'm testing, gives good emission but has blue spot in gun under test (only one gun connected & tested at a time). Filament color a bit warm ? (camera may exagerate this)

Not too clear on picture but the three getter patches are approx 1" x .5" (diminished from factory size ?)

What pictures do you think this would make ? Safe to operate ?

Like most 1st generation tubes, probably had low actual Gun operation hours.

I'm going to ask a stupid question here...

When a tube goes gassy like that, does it have to be rebuilt? What prevents you from heating up the nipple under the tube cap, attaching a new piece of glass, re applying the vacuum, and resealing it? From my view it seems like a lot of these tubes have very, very slow leaks, which makes me wonder how hard it would be to periodically "top up" the vacuum.

-J

The GP22 looks good to me, though the only real test is running it with a chassis. There's no risk involved, either you'll get a raster or a purple neck. What you need is high voltage to check for ionization, I ran my AXP on a CTC-9 chassis because the 4 chassis was still a long way off from being done.

Since you brought it up though, I do see a faint glow between the G1/G2 elements of a good tube under test so maybe it is normal. It's a different kind of glow though, the kind of color you see from beam tetrodes in operation- a more bluish hue.

A lot of gas will have gotten adsorbed (that't correct with the D) in the
electrode surfaces, and even if you stop the leaking process, continued
operation will keep releasing gas inside the tube, and the getters (already
weakened by the initial leak) will not be able to cope with all that gas.
When the tube is rebuilt, it is heated while being pumped out, and
this is done before the new getter is flashed, so that much of the
adsorbed gas is removed, and the (new) getter can do its job after the
tube is sealed. Regards.

I once heard of a high vacuum CRT that had a pump on it, but I think it was only for demonstrations.

Here's an old one with a pump:

www.earlytelevision.org/prewar_crts.html#pump

That would be great if this can make pictures ! What are the present sizes of the getters on your GP22 ?

On one of my 15GP22s, the getter is basically faded to invisibility. Yet it tests strong on a CR70 and looks fine in the TV. As miniman82 sez, the TV is the best tester of all (and the only one I really care about).

Phil Nelson

These positive impressions are hopeful; now onward with the chassis Re-Cap !