Found: 15GP22 (I think)

[kvflyer]

Originally Posted by ohohyodafarted

I have seen a LOT of 15GP22's in our quest to attempt a rebuild. A good set of getters would be silver to possibly charcoal gray wtih some silver in the margins. I have seen getters that look just like these before. The tubes with getters like these were leakers. IE: they had too much air in them to function.

It is likely that when you apply voltage to the filiments, they will either light dimly and/or burn out.

There is always an outside chance that I am mis-reading what I see in the photos, but I would not be optimistic. I have seen bad tubes with getters that look far better than the ones pictured in these photos. Still, you will need to test it anyhow to tell for sure.

Believe me that I am not an expert. But looking at the getter flashing inside of the neck of the tube kinda looks as though it has leaked. I don't see the bright silver and charcoal gray. But that being said, I am NOT trying to rain on the parade. I sincerely hope that this tube tests NOS.

Best of luck, and I look forward to more on this thread.

[AdamAnt316]

Originally Posted by Dave A

Does anyone remember a trick using a neon transformer to test a tube for gas? I saw it once years ago and the interior lit up purple...gas.

No pictures of the method used, but this page should give a good idea:

http://www.theodoregray.com/Periodic...NobleRack.html

[N2IXK]

Applying 6.3V to the heater and measuring the current will find a tube with a lot of air in it.

[David Roper]

?? Does the filament's current draw change in an atmosphere vs. in a vacuum (prior to vaporizing)?

[N2IXK]

The filament will draw considerably more current in air than in a vacuum, because the air molecules help carry away the heat, keeping the temperature (and consequently the resistance) of the filament from rising as much as it would if insulated by a vacuum. This is the principle behind the Pirani vacuum gauge:

http://en.wikipedia.org/wiki/Pirani_gauge

The best way to do this test (without risk of burning the filament out if indeed the tube is a leaker) would be to use a constant current power supply, set for just over the rated filament current (1.8A for the 15GP22). Apply power, and allow several minutes for warmup (with current limited, the filament will be very slow to come up to temperature). Then measure the voltage drop across the filament. It should be ~ 6.3V. If considerably lower, the tube has a very appreciable gas content.

Note that this simple test will not detect lower levels of gas that could impede tube operation. But it is a simple way to identify a tube with a gross leak.

[Eric H]

The flash may be making those getters look thinner than they actually are, hope that's the case at least.

I've seen B&W tubes with the getter so thin you could see the loop but they still checked and worked fine.

[old_coot88]

Originally Posted by N2IXK

Note that this simple test will not detect lower levels of gas that could impede tube operation. But it is a simple way to identify a tube with a gross leak.

In the case of a gross leak, if full heater voltage were applied, the entire base of the CRT will get abnormally hot very quickly due to heat conduction of the air inside.

[reeferman]

In reply to Dave A's question about testing for gas the neon transformer the answer is a resounding YES.
When I would take duds back to Olive Electronics, Don would pull out this high voltage generator that looked like a HV probe.
He'd zap the neck of the tube and ask all present if anyone wanted their piles treated.
Nice guy, but I never turned my back on him.

[jr_tech]

Originally Posted by old_coot88

In the case of a gross leak, if full heater voltage were applied, the entire base of the CRT will get abnormally hot very quickly due to heat conduction of the air inside.

Not for long, however as the heaters are likely to "burn out" fairly quickly due to the higher than normal current flowing through them... been there, seen that.

jr

[tvdude1]

Ebay the tube. Take a chance you cant loose.

[Electronic M]

Originally Posted by reeferman

.
He'd zap the neck of the tube and ask all present if anyone wanted their piles treated.
Nice guy, but I never turned my back on him.

What the heck are 'piles'?

[mstaton]

Hemorrhoid's

[old_coot88]

Originally Posted by jr_tech

Not for long, however as the heaters are likely to "burn out" fairly quickly due to the higher than normal current flowing through them... been there, seen that.

jr

Right you are. Been there, seen that likewise. 'Cept with regular tubes moreso than CRTs.

[Eric H]

Color Bar generator discussion moved to this location:
http://videokarma.org/showthread.php?t=260205

[bandersen]

I brought my trusty Sencore CR70 to the ARCI Radiofest earlier today and helped oldradio99 test the 15GP22.

At first we had good filament glow but no emissions or cutoff on any gun. After about 10 minutes the filament current drop dropped because one of the three filaments burned out. A short while later the draw dropped to 0 as all the filaments stopped drawing current. It seems that indeed it had gone gassy.

So that's a shame but at least it's in good condition and maybe can be rebuilt one day.

I stayed there until late afternoon chatting with fellow collectors (ElectronicM and Wiscojim mostly), and had a great time. Unfortunately though, I left my CR70 in Wiscojim's van I'll try to swing by tomorrow and pick it up otherwise I'm sure I'll get it back eventually...