Securing a loose anode cap ?

[beam me up schottky]

Recently I managed to find a good used PEN DD61 valve for my pre-war Philco. As many may realise this is a very rare valve.
The only problem is that the anode cap is very slightly loose.
Is there an accepted method for making it secure ?
My first thought was to very carefully apply super glue around the flange of the cap, allowing to creep underneath it but then realised this may not be heat resistant.
The problem with any adhesive is finding a suitable type that is heat resistant.
Would unsoldering the cap to more easily apply a suitable heat resistant adhesive be viable ?

[OldTickTock]

Superglue is a no no, it will cause the envelope to crack. I have repaired lots of anode caps with araldite, it was recommended to me by ex trade. I've used it on many CRT base's too, all successful.

The last valve anode cap I did was for a PL36 line output valve for a PAM521F TV, it's still working fine. The last CRT base was last week when I repaired an old Mullard CRT base to the neck,that has spent 10 years in a garden

The trick is not to apply lashings, it does not need it as it provides such a good bond, do it sparingly. I use a cocktail stick it allows me to apply a thin controlled line of the adhesive.

Chris

[tiv48]

agree i have used araldite with no problems
rob t

[Joe]

Wasn't the original cement wood-flour and shellac? As you say epoxy is fine and I'm chiefly just curious as it's always interesting to know how things are/were made.

- Joe

[Skywave]

So 'Superglue' is a no-no for this type of repair, eh? Well, well, I never knew that! And to think that I too have a few valves that need such a repair - and that picking up a bottle of Superglue would have simply been an automatic knee-jerk reaction. :s
Araldite it is then! No problem.

Probably the useful tip I've learnt this month; thank you.

Al.

[beam me up schottky]

Well you can't dispute experience ! I will perform the minor surgery and report accordingly, hopefully the valve will emerge still functioning, it took me ages to find one ! Thankyou Chris for the information.

[OldTickTock]

Just for clarification

"The January 2003 issue of the excellent American magazine 'Antique Radio Classified' contains two letters warning about the dangers of using cyanoacrylate glue, with trade names such as Super Glue, for repairing valves.

Restorers often need a fast-curing glue for cementing loose glass into valve bases but danger lurks here. The problem is the difference in the coefficient of expansion of glass and of the cyanoacrylate will cause the glue to act like a hot wire glass cutter - cleanly cutting the glass off at the base when the valve heats up to full operating temperature.

The bottom line is never use this glue on any valve or tube that runs too hot (when up to full temperature) to hold your hand on the tube. This means no power output valves and no rectifiers. However, this glue is considered safe, with some reservations, for battery valves and most small signal valves, if they don't get too hot."

I would just avoid it at all costs, even on battery valves, it's unforgiving too when manipulating. Araldite gives you time to position secure and remove excess with the appropriate cleanser.


The recommendation for Araldite came from a very well know TV engineer in West Sussex.

[Yorkie]

Wasn't the original cement wood-flour and shellac? As you say epoxy is fine and I'm chiefly just curious as it's always interesting to know how things are/were made.

- Joe

Yes Joe - got it in one.

If ever you wish to remove a valve base or top cap (having unsoldered the connections such as at the valve pins or top cap of course), if you soak the base or cap in meths, which is a solvent for shellac, it will dissolve the cement and you can tweak the base or cap free. To make up a similar cement, you need a small amount of shellac (French polish or shellac sanding sealer - NOT cellulose) and some wood flour, which you can obtain by using say 80 grit sandpaper on a piece of scrap wood. Make a stiff mixture, and use some elastic bands to hold the top cap or valve base in place overnight until the cement sets.

Initially, when rehabilitating an EBL31 valve, I tried cellulose thinner as a solvent for the original cement, which didn't work. It was only when I researched it further that I learnt that originally, they used shellac and wood flour and that meths would dissolve the cement, as indeed it did, though no doubt as time progressed - in the post-war era - they used other types of cement, perhaps epoxy based, were used.

If using Araldite, various types have various upper temperature limits before they will dissolve, so if the valve is going to get quite hot, it's worth checking the spec. I'd concur with advice about not using superglue as it isn't flexible, and I've heard of cases where (allegedly), it has cause the glass to crack on heating up. Whether htis is just an 'urban legend' Ive no idea but on a rare and costly valve, it is't something I'd want to put to the test.

Hope that helps.

David

[Joe]

I don't generally trust cyanoacrylate as far as I can see it in general and it tends to be my last resort adhesive. It is good on some types of plastic though but that's Russian roulette as it's hopeless on others. It doesn't seem to widely realised either that, at least in general, it isn't water-proof.

As well as anything else the fumes coming off a top cap as it heated up would be far from pleasant.

Good luck with your repair. As Chris showed with that CRT the age of miracles isn't over.

- Joe

[Brianc]

If you are too lazy to make some wood flour, Polyfilla works just as well. It saves a lot of messing about. However, If you have a few cabinets to re-finish, you could kill two birds with one stone -make wood flour and make shellac for both the valve and the cabinet!