A CRT went to air
 

Well this sucks, 3 or 4 years ago I bought a wreck of a 1950 GE 12", turned out it had a 12KP4 that tested good.
I parted the set out and stuck the CRT in my storage room where it's been sitting for the last couple years, I've been cleaning up around here and decided to give the tube a bath since it was filthy dirty, before I did I wanted to retest it and make a note of how well it tested.

As it turned out when I hooked it up the first thing I noticed was the heater seemed dim, I also couldn't get the Cutoff to adjust, I knew this tube had checked OK so I bumped the voltage up a bit to 8 volts, the heater got brighter but still no cutoff or emissions, then I noticed the Getter, it basically wasn't there, just a slightly cloudy film where it should be, also the heater kept getting dimmer and finally quit so I knew for sure what had happened then.

I pulled of the base cap, it was loose to start with and I thought maybe the evacuation nipple had been broken somehow but it was in perfect shape, in fact I found no definite cause of the problem except some suspicious looking areas where the wires go through the base.
Finally I snipped of the nipple to see if any vacuum was left, there was still quite a bit but not enough for it to work or even keep the heaters from burning out, I guess it just decided to leak after being disturbed when I took it out of the set, 63 years old I guess anything can happen.

So it wouldn't be a total loss I decided to see if I could fix the loose base on the 12" Philco I just bought, that base came off really easy since there was really only one or two wires still soldered to it, fortunately all the wires from the CRT are intact, however there's so much of the glue still wrapped around them I decided it would be a disaster to try and remove it.

It was easy enough to get the wires threaded through the new base but when I tried to push it over the glue it was a bit too tight and it broke the base in several places, luckily it didn't hurt the CRT, but now I need another base cap to try again and I don't have any tubes dead enough that I would want to junk them for a base.

This picture is of the good Philco tube, I think it best to leave the glue alone and just add some glue to the new cap, after I grind it out a little so it will fit easily over it.

Use the plug from an old CRT booster. Most of those are standard CRT bases.

(Watch out for the few that were made of soft plastic, which won't stand the heat.)

Jas.

I have noted over the years it is not uncommon for a small percentage of used or even NOS tubes to go 'to air' (gassy) after an initial thermal cycle or two. I suspect it is the same with CRTs, though the number of CRTs I have dealt with is only a tiny fraction of the number of tubes I have dealt with. My guess would be microcracks around the base pins, created perhaps at the time of manufacture, or later due to stored stress in the glass, or maybe corrosion of the wires.

No matter the cause, it take very little air in a tube (CRT or otherwise) to overwhelm the getter and ruin the tube.

In the process of our 15GP22 rebuild efforts Bob and I have opened many 15GP22s with white cursty getters and often burned out filaments. I thought these tube were "down to air", that is full of air. Bit in every case, there remained a considerable amount of vacuum in the tubes. None of them were at ambient atmospheric pressure.

Just my observation....

I had several good, used CRTs stored in an outdoor shed for about 5-7 years. The temperature swing would go from about zero F to about 100 degrees F. I was very sad to find that two had gone to air. Bugger! The gent that I had gotten them from ran a TV shop years ago and he had stored them indoors. Thankfully, the 21CYP22 that tested NOS was not bad.

I now am a firm believer that these CRTs and for that matter, NOS vacuum tubes should be in a controlled environment.

Sorry that your CRT "Went South".

Hmmm - you would have thought that since tubes have heaters that get very hot, a few degrees of cold below room temp wouldn't bother them. Interesting and disappointing.

My tube had been stored inside since I got it, before that I have no idea but judging by the set it was in, outdoors, or at best is a garage or patio for a long time.

IMHO, All vacuum devices leak! Some leak at a slow rate, some faster. The getter can handle a slow leak rate for decades or longer, but when the getter is used up, it is "game over".
jr

Apoparently this one holds an exceptionally good vacuum.
"Look Ma no getter!"
:bigok:
http://www.centennialbulb.org/photos.htm

Light bulbs only have two leads going through the glass, most CRT's have 10 or more, plus the Anode Button, not counting the ones that are metal/glass composites.

It's a miracle any of them last more than a few years.

This one hurts more because it was an Aluminized tube, and I have a couple three 12" sets in need of good tubes. :sigh:

That was prolly a brain fart on my part. The bulb more likely has inert gas at low pressure, not a hard vacuum. Dumb, dumb.:o

No mechanical system is perfect, all leak, like you said. That goes for vacuum systems to refrigeration systems, some leak a ounce a minute, some a ounce in 30 yrs.....either way they still leak.

It really sucks to lose one. :sigh: I recently moved my small stock of backup crt's from the attic to room temp storage. I figure one less variable to deal with. Automobile tubes come to mind - but I suppose back in the day it was no big deal if one failed now and then from the extreme temp variations. I have a sneaking suspicion that repair shops and distributors of tubes often stored them in un-climate controlled buildings. At least that seems to have been the pattern here in WI.

I can relate to that. I had a new old stock 16AP4 saved to use in an RCA I haven't finnished. Three months ago I went to carefully move the tube, and, I picked up the neck, and, the rest of the tube stayed where it was. Boy, did that upset me!
Bill Cahill

Was there a big "Whooosh" or had the tube totally gone to air before you picked it up?

jr

It had already gone to air.
Bill Cahill