The one constant I have been seeing is all the roundie crt sockets seem to be coming loose due to the age of the glue used to secure them when they were manufactured. Anybody aware of what type of adhesive they used when manufactured? My guess is it was some type of epoxy.

Sorry, I thought you were addressing the socket, not the CRT base.

What ever was used is now long gone, for sure. My best results have been using the regular JB Weld. Apply glue to clean surfaces, place the item in the oven, set at 170 degrees. When set-point is reached, turn off oven and allow to cool while in oven. Works every time.

There was a special cement used to glue the base onto the tube, I don't know if it's made anymore. RACS in France used electronics safe adhesive, similar to silicone just without the corrosives in it. They drilled a small hole, and injected it through the base pin- that's what I would do.

There was a special cement used to glue the base onto the tube, I don't know if it's made anymore. RACS in France used electronics safe adhesive, similar to silicone just without the corrosives in it. They drilled a small hole, and injected it through the base pin- that's what I would do.

The special silicone sealant without acetic acid probably isn't a product that you can find on the shelf at your local hardware store. Any suggestions as to where we can find it, I have many tubes that could use it, not just CRTs.
Thanks,
Kevin

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The special silicone sealant without acetic acid probably isn't a product that you can find on the shelf at your local hardware store. Any suggestions as to where we can find it, I have many tubes that could use it, not just CRTs.
Thanks,
Kevin
How about the "sensor safe" silicone sealant sold at auto parts stores?
jr

How about the "sensor safe" silicone sealant sold at auto parts stores?
jr

I'll check it out. Thanks for the suggestion!

And how the heck did I wind up with two names on two different computers?! I'll check that out, too!

...

I have bought that before, and it had the same acidic smell that standard silicone has. It may lack other additives that could be harmful though.

Darn, several people here have recommended the "sensor safe" material... and it appears to be MUCH cheaper than Dow Corning 3145, which I believe was used in some CRT factories. Anybody know what the hard orange-brown cement commonly seen in base caps onolder tubes was?
jr

I wouldn't use any kind of silicone sealants. If for no other reason the stuff is not rigid when it cures. They make a world of two part (I guess) epoxy type products like someone mentioned J-B Weld. But I wouldn't have thought of that. I would go for the plastic two part stuff or maybe better yet super glue.

The sockets get loose often from being not so gingerly separated when the set has been worked on. You have to hold the plug on the end of a c.r.t. tightly and gently wiggle the socket off. A shot of WD-40 or any other penetrating oil on the pins helps. If it's still stubborn, you can gently wedge with a medium screw driver working your way around the circumference.

I use Permatex 81730 Flowable Silicone Windshield and Glass Sealer which does not contain acetic acid and is designed to bond well to glass. It holds the base on tightly but has just a little give to it.

It's my understanding that using a very hard adhesive like epoxy could cause the glass to crack if it has a different coefficient of expansion. Those necks can get pretty hot during operation.

Way down at the bottom of this antique wireless article they give an old RCA formula for "tube basing cement".

http://www.antiquewireless.org/uploads/1/6/1/2/16129770/10-the_vacuum_tube.pdf

Coarse marble flour 170 lb.
Orange flake shellac 19-1/2 lb.
Durite phenolic resin LR275-2 7-1/2 lb.
Medium - color (grade G) rosin 3-1/4 lb.
Denatured alcohol 9 liters
Malachite Green aniline dye 10 g.

(Just for reference: the above recipe yielded enough cement to put bases on
23,000 Type 50 tubes. The dye gave a rough indication of curing temperature by
losing its color near the desired 150ºC....

I sure wish I had 23,000 type 50 tubes to try it out on :D

I've had great success for years with clear fingernail polish. Holds up to the heat well.

It had been referred to me by a through a radio/ham guy to use some Elmers white glue. Although you need to allow time to let it set up, I've been suprized by the results. No kidding!

It's my understanding that using a very hard adhesive like epoxy could cause the glass to crack if it has a different coefficient of expansion.That makes a lot of sense to me; I am in the non-epoxy camp. Silicone holds on the cap just fine for my purposes, which do not involve violently yanking on the ends of CRTs. If you ever meet someone who does not know how to grasp the base of a tube when plugging or unplugging it, send 'em to me for a tutorial :)

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

I managed to get one CRT rebuilt by Hawkeye before they shut down and Scotty used some type of silicone on the base. I've found that a few tight turns of electrical tape does a nice job of holding a loose base on while testing a CRT.

It had been referred to me by a through a radio/ham guy to use some Elmers white glue. Although you need to allow time to let it set up, I've been suprized by the results. No kidding!

That makes sense. That glue actually softens up when it's heated. You would want to be careful not to pull the socket off when the tube is hot.

Sensor safe, that's the stuff I was thinking about. I've seen regular silicone eat through traces on PCB's, that was enough to make me look for an alternative.

There has been countless discussions of this topic on the Antique Radio Forum. The one thing that I came away with was that unfortunately Super Glue has a different temperature coefficient and has been known to actually crack the glass envelope of a tube and even pull a piece out of it. So, it is frowned upon.

With signal tubes, Elmer's Glue was mentioned many times. But tubes that get very hot, like power pentodes, rectifiers etc. may find it to be improper.

Several have suggested using sensor safe silicon sealant. No real negative advice against it.

As Bob has mentioned, a good wrap of black electrical tape will secure the base whilst you are testing the tube. You certainly don't want to flex the base and break off the wires at the glass seal!

BTW The clear finger nail polish worked great on the crt base