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Originally Posted by wiseguy
well its been several hrs since i called them.
no return call..so i called them a 2nd time,this time a guy answered and didnt speak very good english at all,as a matter a fact i had to ask him to repeat what he said..finally he said.. "someone will call you back about 5:00-5:30 pm". click
maybe they dreamed they could rebuild the 15GP22?
kinda like i dreamt last night my Male cat had kittens.. 
terry |
If you get a hold of someone (guess you've already figured out not to hold your breath...) and you get a price I think it might be a good idea to find out just what these guys are doing. Why not ask or email them for details. After all, you got a rare tube. Here're a few questions I would ask:
1) Physical damage to the tube face plate - if so then it may not be repairable. Any scratches or chips may cause tube to implode of crack during baking. Then again, it may not. Just all depends on the damage and where. For a sizeable chip of glass out of a corner of the tube may be courting disaster!
2) Is the tube at air/low vacuum/condition of the getter (silver or white)?
If tube is still under vacuum and getter is silvered then:
What is their inspection process?
If tube is at air do they break the seal cut off the old gun assembly?
and then connect the open funnel stub to a vacuum chamber to do a
slow outgas pre-bake at 150 deg C to drive off water vapor?
It's a hell of a lot easier to pull water out of a 2" stub than a 1/4"
evacuation nipple to pressures of at least 10-6 torr!
3) What's their experience rebuilding the 15GP22? References?
4) What's their rebuilding process? In house or RCA?
5) When they break the seal to start the process do they do it vacuum?
6) Once the seal is broken do they back fill the tube with dry N2 gas?
It may be necessary to physically handle the 15GP22 by hand unless
the rebuild chamber can accommodate the tube easily and be kept
under vacuum at all times.
7) How do they alignment of the gun with the phosphor plate?
8) Do they know which gun goes up?
9) Where did they get their replacement gun assembly?
10) Are they capable of rebuilding the electron gun with new filaments?
11) How do they prepare the tube?
12) How do they prepare the replacement gun?
13) What maximum temp do the bake the tube?
There is no need to exceed 300 degC. Maximum tip off temperature used according to RCA research papers described limiting the original manufacturing process to this temp for the 15G. I would suggest not exceeding 200 DegC but, instead, allowing the tube to bake for a day then gradually reduce to room temperature over 7 days.
14) Are they doing anything special to prevent thermal shock to the phosphor plate?
15) Do they thermally cycle the tube? If so, periods and ramp times?
16) Do they do local annealing of the new glass seal on the gun assembly?
17) What is the maximum tip off temperature during baking?
18) Do they helium leak test the face plate to cone (funnel) seal?
A helium leak test of the feed throughs at the gun base after a replacement gun it critical to make sure the replacement seals are good.
19) Are they able to place a 20KV charge to stress test the tube?
The ability to stress test while actively pumping the tube before sealing allows the rebuilder to further outgas the tube. Especially since these tube have been sitting around for 50 years.
20) How long do they evacuate the tube before sealing?
I suspect that attempts to build these tubes in the past have failed not because of the gun replacement parts (...don't rule anything out though!) but because of suspect improper evacuation, outgassing and stress testing before sealing the tube before finally firing the getter. In my mind, there's no reason why a 15GP22 can't be easily rebuilt. However, if the tube rebuilder thinks they can do a regular 'slap and dash' job like on a modern all glass CRT then it ain't going to be so! Success takes time, exceptional vacuum technique and extreme patience, especially with the rebuilder taking their time not baking the tube to the point where seals and/or phosphor plate are damaged.
Anyways, give it shot. Let's see what they say.
Tom