Re-bonding tube bases

[Mick Bailey]

I've read of quite a few methods/materials - nail polish, cyanoacrylate etc. but none of these are rated at tube operating temperatures - particularly where a tube is mounted upside-down and the base is getting heat-soaked. I've tried using acetone as sometimes recommended but have not achieved any success. I've also seen tubes with a fillet of silicone but this doesn't look good to me, particularly with NOS tubes (perhaps a loose base is one reason why some ended up being NOS in the first place....).

My thoughts are there must be something better - maybe a silicate-based adhesive such as that used to cement rope-seals around wood stove or furnace doors.

Does anyone have a proven, permanent method that will stand up to the temperature and still hold?

[tedmich]

McMaster Carr has 3 high temp electrical epoxies, but they are quite expensive
7563A24 500ºF
7563A27 600ºF
6196T1 450ºF

While tubes can get to 450F I think the base is much cooler and you could probably use std electrical epoxies. You'll want to avoid metal filled adhesives which will short the HV! The (non-acetoxy!) silicone could work but the typical acetic acid chemistry corrodes electrical contacts badly.

[Tom Phillips]

Even though they are not rated for high temperature applications, I have found cyanoacrylate type adhesives to do an adequate job.

[dai h.]

Would high-temp RTV work? (I've never tried it myself, but have seen it recommended to fix a cracked vacuum tube.)

[The Dude]

I've used RTV on bases and it worked fine. I wouldn't use it to fix a cracked tube. At some reasonable point you just replace them.

[Mick Bailey]

There was (is?) a company selling a specific product;

REPAIRING LOOSE BASES OF OLD ELECTRON TUBES

I've got 28x NOS 807s, all with loose top caps and bases, plus loads more NOS audio tubes that need fixing. Plenty of stuff to do some experimenting with. Some of the 807s have ceramic bases and would be a good candidate for thermal testing.

[riz]

Mick, I've never tried it on tubes, but maybe this stuff in the link will work. Really thin silicone.

Sealants : Permatex® Flowable Silicone Windshield & Glass Sealer

I've used CA myself with decent results (3 years and running) in my Champ. The 6V6 tube I found in my Grandpa's garage and I just had to save it!

[g1]

There's no guarantee that everyone will grip the tube by the base for removal. Any flexing will be bad for the connections. So I think if possible a hard compound is preferable to a non-hardening semi-flexible solution.

[J M Fahey]

A hard adhesive looks better but does not attach well to smooth pore less glass.

Use RTV which although somewhat flexible grips very well to glass and stands high temperatures.

Personally I have used Industrial grade Epoxy, which barely stands the temperature, not as an adhesive but as a filler.

A ring all around stops wiggling, which is the main problem.