I am glad to see some fruitful and informative discussion going on here.

Matt

21" Predicta CRTs can be rebuilt with standard 6.3v gun - They work just as good.
Had one done this way at Wisc Picture Tube when they were open.

70's Guns, A56-120X CRT's etc....
 

Whatever you do--DONT cut up/use for parts 70's Euro guns,--Not unless you have thousands of 'em!

Colour TV only started here in the UK in Late 60's and the tube range was rather limited, consisting of 19 to 26" Delta type rectangular CRT's such as the A56-120X
--That tube was probably THE most popular CRT in Europe from the start of colour till the mid 70's when PIL came about I guess, prob Millions made, by a few different makers, and still hundreds of thousands rebuilt by loads of Co's.

Can I ask--Do you know if you have any guns for the A56-120X colour CRT from early 70's?

--For the European collectors market these CRT's would need to be rebuilt--Ive got four of these CRT's and not one is what could be called--Good.
--Just a huge shame shipping to and from US to Europe is so expensive!

Maybe worth giving these guys a shout for cathodes and heaters--
http://in1065131610.fm.alibaba.com/p..._Cathodes.html

Us yanks had the same shipping cost problem back when RACS was the only one rebuilding classic CRTs...

I don't know if we have those guns. We are still trying to figure out what came from RACS.

At a guess,--You probably have--being that RACS was a French CRT rebuilder, these type delta gun tubes were just as popular there I think, as here.....
--How you would recognise them if there's no part-numbers on boxes etc and with 4 tons of stuff to go through--I guess time will tell.

When I worked in South Africa in the 80's I spent a day in the CRT rebuilder plant of the Co I was with, (Teljoy, Jo-Burg). Most interesting, wish I had taken pictures and more notes!
--Only thing I remember them saying was that the CRT needs to be only down to air for less than 24 hours--enough time just to change the gun, get it re-sealed and pumped--something to do with the phosphor, although no idea why....

The phosphor won't be contaminated by moisture, I think that was pretty much proved by the 15GP22 rebuild RACS did for the museum. Bake out removes it all anyway. I don't know if there are any delta guns in the RACS stash, the tubes they rebuilt for the French railways were all inline.

If a CRT is going to be down to air for any length of time (days, not hours) it's a good idea to rough pump it and seal it off. While the phosphor shouldn't suffer it's just a simple and sensible precuation. No need to bake the tube or use the diffusion pump.

For the same reason I'm keeping all my duds sealed up, plus it keeps me from mixing up the guns!

If the tube has leaked completely down to air, then I'd look into filling it with a noble gas until it could be rebuilt.

I don't think we need to go to much trouble to protect the phosphor. The 15GP22 that was rebuilt by RACS and is at the museum was open and full of cobwebs for years. It turned out fine:

http://www.earlytelevision.org/2010_...tion_RACS.html

open to air
 

Leaving the tube open will degrade the aluminized coating on b&w tubes and the aluminum coating behind the phosphor on color tubes. Black matrix color tubes are even more sensitive.

It also depends on the temperature and humidity.
Black matrix color screens will get blotches on the screen within 48 hours on a hot, humid Ohio summer day. A non matrix screen will survive from 3 days to a week. A b&w aluminized tube will be garbage after 2 weeks.

We just told you a 15GP22 was open for years.... no damage.

The face has some dark blotches in the phosphor so not exactly "no damage"...Still ignoring the blotches it did hold up rather well.

I believe the blotches were from dirt and debris that fell into the tube, not air or moisture, though I can imagine that extremely humid conditions could probably cause problems.

As far as the Aluminizing breaking down I doubt that would happen, it's done with the same Aluminum vapor depositing process as the parabolic mirrors in projection sets and they survive in normal atmospheric conditions for decades, it is in fact quite a tough coating based on my experience in trying to remove some of it from a mirror.