Keeping a 15GP22 alive

[Red Raster]

Took a trip down South picked up a Radiola 3 and a 15GP22 The CRT checks good using a Sencore CR70 (no purple haze) My question is what is current best practices for preserving the vacuum.

[DavGoodlin]

Having no experience with such an artifact, one thing does come to mind.
It IS metal and glass, with differing expansion rates, so store in a location with the temperature moderate with no extremes of humidity or vibration.
You're on the right coast for that

[colorfixer]

Presuming the vacuum in the tube is still sufficient to allow the tube to work...

There's been a number of ideas mostly predicated on failure of the rather large metal to glass bonds. The concept was originally to apply a sealant like Vac-Seal to the seams.

However, a number of fellow enthusiasts have found that the weld between the two metal sections comprising the ultor ring is also a point were leaks can occur. In this case, nickel plating the ring would theoretically seal the micro sized leaks in the weld.

Good luck.

[Electronic M]

May as well play a continuous loop of the Bee Gees' "stayin' Alive" too...So far it seems that when they fail they fail with little rhyme or reason despite some preservation attempts.

[benman94]

All practical seals leak to a degree, even the good 15GP22s are leaking to some extent right now. It's when the leaking outpaces the ability of the getter material to maintain the vacuum that you run into trouble.

I keep my CT-100 at a consistent 62 degrees with ~30% relative humidity. I reason that the less the metal and glass expand and contract, the more likely the seals are to remain more or less intact. I have no idea if it's actually doing any good. Beyond that, I'm crossing my fingers like anyone else.

[wa2ise]

Back 30 years ago I used to work at an R&D lab, and other researchers used an epoxy like stuff called "Torr Seal". For fixing vacuum leaks. It dried to a hard surface, and presumably was made to not outgas. Looks like they still make it: https://www.lesker.com/newweb/fluids...?pgid=torrseal No idea what it costs...

[Eric H]

No matter what you do the tube is going to go through hot cold cycles if you use it.

I would think very cold temperatures would be the more harmful since the tubes were manufactured under very hot conditions, but that's just a theory.

I think if I had a good one I'd just handle it as little as possible.

[miniman82]

A CRT tester is NOT the end all of testing when it comes to vacuum leaks, and you certainly wouldn't be able to tell if there's a discharge glow in the neck from using one- that only occurs with the application of HV from a running chassis. So unless it's made light with a CTC-2 chassis, what the tester tells you is anecdotal. It would be reassuring to see shiney getters in the neck, but at the last convention I went to there was a 15G with ugly ass getters that still worked fine so it's not a written in stone kind of thing.

As far as how to treat it, the museum doesn't have a fancy HVAC system, and the tubes there seem to be holding up fine. As long as you don't ding the weld rim, it's just another vacuum tube in practical terms and you shouldn't treat it like ordnance anymore than any other tube. If it's gonna leak it's gonna leak, nothing you can do about it. That means as long as it has vacuum you should enjoy it, or get it to someone who will enjoy it till it dies. Nothing more sad than a 15G that went to air with little hours on it...

[Red Raster]

I have had this set for five years and have yet to power it up. This weekend I will examine the chassis further and apply power with a variac after I am certain I will not cause any damage i will go to town on the capacitors. My goal is to get a raster and really see how good the crt is. For the good news is the chassis is very clean and looks like it has seen little use and furthermore all of the tubes are original and test good except one with the purple haze.

[Red Raster]

Originally Posted by miniman82

A CRT tester is NOT the end all of testing when it comes to vacuum leaks, and you certainly wouldn't be able to tell if there's a discharge glow in the neck from using one- that only occurs with the application of HV from a running chassis. So unless it's made light with a CTC-2 chassis, what the tester tells you is anecdotal. It would be reassuring to see shiney getters in the neck, but at the last convention I went to there was a 15G with ugly ass getters that still worked fine so it's not a written in stone kind of thing.

As far as how to treat it, the museum doesn't have a fancy HVAC system, and the tubes there seem to be holding up fine. As long as you don't ding the weld rim, it's just another vacuum tube in practical terms and you shouldn't treat it like ordnance anymore than any other tube. If it's gonna leak it's gonna leak, nothing you can do about it. That means as long as it has vacuum you should enjoy it, or get it to someone who will enjoy it till it dies. Nothing more sad than a 15G that went to air with little hours on it...

It was time to see if my CT-100 has a working 15GP22, After carful examination I powered up the set with a variac starting at 60 volts slowly advancing the voltage, Around 80 the neon tester lit up brightly as I held it close to the horizontal out put plate cap. Pushed the ac voltage higher, Looking at the screen and then the neck answered the 64,000.00 dollar question, I saw a reddish raster (Go figure) and no purple glow in the neck. with full deflection and the scan lines in focus.
This was just a short duration test without signal and now the chassis will under go a thorough re cap job before it gets plugged in again. The long and rewarding journey has started.


It's alive and will be a working set after restoration.


This is the chassis I have to work with I have yet to clean it.


All of the tubes check good and they are the factory originals.


62 years of dust.


These selenium rectifiers are good and allowed for a successful first
light test.

[Phil Nelson]

Man, apart from a little dust, that's a mighty clean looking set.

Take your time and enjoy the project. Most collectors don't get a chance to restore more than one of these!

Regards,

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

[kvflyer]

Congratulations!! I would be remiss if I didn't say that I was envious. Enjoy that set. Not too many people out there understand what this is all about... especially what the 15GP22 is all about. I didn't until a few years ago...

[dtvmcdonald]

You are a very lucky man! I don't have to be envious, as I have a very nice one.

I'd love to see pictures of the set's bottom. Those pots on the top have very
long stems and look like they are replacements. That's a good thing, as the
short ones are hard to get to with the chassis in the cabinet.

Note that McVoy convinced me that the very low voltage electrolytic 2C107
(1000 uF 3V NONPOLAR) need not be replaced, and he was right. Leave it be!

Note also that there are production changes in that part of the circuit (around 2C107)
which you need to be aware of.

BEWARE! of the resistor value of 2R242, in the first convergence amp plate. RCA says 270K, Sam's says 27K. 270K simply cannot generate those voltages, verified by my direct measurement. 27K can, and works, but my convergence pot is set at the
absolute top of its range. I suggest 35K.

Good luck with the usually bad white peaking coils. Don't try finding exact replacements. I do not suggest using the "usual suspect" old Miller or Meissner
replacements for the larger value ones but rather modern ferrite core ones. The
6.8 mH one might better be replaced with a smaller one, like 4 mH. If needed I can look
up the part numbers of the ones I finally selected from an assortment of old and modern ones I bought when I restored mine two years ago.

Also ... if you have and are good with a scope, I strongly suggest running the recapped chassis on the bench, and doing sweep generator tests
of all the areas with those nasty coils, before you declare victory over them. Different
coils with the exact same inductance value can generate hugely different responses,
with hugely different picture responses. You can make the Q response quite a bit
flatter than the traces in RCA or Sams, and the picture difference is quite a bit too.

Another tip ... while working on the three color amps (with may of those coils),
check each and every color/luminance matrix resistor and replace any that are
more than 5% off. If you send me a private message I can send you big pile of
test images especially designed for the CTC2 chassis and its matrix.

Finally ... if yours is like mine, I suggest a long chain of 5W 200V Zener diodes in place of 3R260.

As others have, have fun and be fastidious!

[Kevin Kuehn]

Your sets 62 years of dust looks to be about the equivalent of 1 year around here. It always amazes me how little dust some peoples homes have. Very exciting adventure you're on now.

[Pete Deksnis]

Originally Posted by Red Raster

...the chassis is very clean and looks like it has seen little use and furthermore all of the tubes are original....

Since that's the case, perhaps under that dust there's an actual pristine set, meaning that it has spent its 62 years not subjected to the vicissitudes of weather. If that's the case, then it's possible that all the white inductors are perfectly sound and need not be replaced, giving you a rare CTC2 chassis replete with production inductors.

I was fortunate to have acquired such a set and used its inductors to populate my restored chassis. This was ten years ago and the chassis is still running with those 'pristine' white inductors, and that includes one year of use at the Early Television Museum demonstrating the one successfully rebuilt 15GP22.

Pete