One of my 866A tubes lost it's top cap. There is some sort of friable brown spongy material under the cap. I've crimped on a piece of wire (couldn't solder to the tube pin) to the piece sticking out of the tube and will solder that wire to the cap but I'd like to use some sort of adhesive to support things. The temperature is pretty moderate at less than 50C. I was thinking some RTV adhesive but what would you folks recommend?
High temperature RTV silicone
https://www.permatex.com/products/g...-ultra-red-rtv-silicone-gasket-maker-3-35-oz/
https://www.permatex.com/products/g...-ultra-red-rtv-silicone-gasket-maker-3-35-oz/
I had good results with RTV. For small tubes that don't become hot, I use a generic clear adhesive because it is easier to handle.
I used some hi-temp RTV. Thanks for the input. We will see if there are any issues in the future.
I've also used the hi-temp RTV for valve TC and base repairs, and even for suppressing microphonics. The only hassle is that like all silicone tube products, the next time you want to use it a few years later it has gone off. There are other engineering grade silicones with the same hi-temp rating that are often found in building supply outlets, but RTV is the most common and often available in small handyman tubes.
I've had to carefully scrape the surface of the short length of wire exiting from the valve glass to get it to tin properly and then allow it to make a 'solder' connection to the TC solder bath. Not having a soldered joint to that wire seems a bit of a worry.
I've had to carefully scrape the surface of the short length of wire exiting from the valve glass to get it to tin properly and then allow it to make a 'solder' connection to the TC solder bath. Not having a soldered joint to that wire seems a bit of a worry.
Hello,
Just a suggestion for the silicon going bad when stored problem. Put a dab of silicon (likely any quality grease would work) on the threads of the cap before screwing it on. Keeps the air out and usually prevents RTV from setting up over time. FWIW.
Greg
Just a suggestion for the silicon going bad when stored problem. Put a dab of silicon (likely any quality grease would work) on the threads of the cap before screwing it on. Keeps the air out and usually prevents RTV from setting up over time. FWIW.
Greg
Araldite, if needed use ordinary cement 50-50 with Araldite.
Cement cures in 6 hours with Araldite, and works out much cheaper than Araldite 24 hour grade alone.
Useful if you need lots, here a couple of drops would be enough.
Or a similar two component epoxy.
Alternately, high temperature RTV, used for engine gaskets, radiators and son on.
We get small tubes here, about 30-40 grams.
It gets hard in a month after being opened, so buy the smallest pack.
Power line insulators are bonded to the metal ends using a cement based system...they are usually ceramic or glass, and the high voltage ones are big and heavy, they look tiny hanging up in the air.
Cement cures in 6 hours with Araldite, and works out much cheaper than Araldite 24 hour grade alone.
Useful if you need lots, here a couple of drops would be enough.
Or a similar two component epoxy.
Alternately, high temperature RTV, used for engine gaskets, radiators and son on.
We get small tubes here, about 30-40 grams.
It gets hard in a month after being opened, so buy the smallest pack.
Power line insulators are bonded to the metal ends using a cement based system...they are usually ceramic or glass, and the high voltage ones are big and heavy, they look tiny hanging up in the air.
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The adhesive is softened with alcohol. I think it is a mixture of ground stone and shellac, with similar coefficient of expansion as the glass.
All of the tubes I have that had loose bases have been fixed by dunking in a glass of meths, but I have not tried with a top cap.
All of the tubes I have that had loose bases have been fixed by dunking in a glass of meths, but I have not tried with a top cap.
The cap is attached with RTV adhesive. The high heat type. I'm not sure what the last two posters were trying to communicate but thanks!
Water Glass is a powder than can be dissolved in water, and sets as glass, very common.
Cannot dissolve after setting, a reaction takes place.
So a glass like substance is deposited.
Might be useful for this purpose.
Cannot dissolve after setting, a reaction takes place.
So a glass like substance is deposited.
Might be useful for this purpose.
The original substance is made of phenolic (iditol) resin plus fillers (marble dust). Sets when baked. I would not use water glass (silicate) based glue - it reacts with the glass itself - otherwise it would of been widely used in light bulbs and such. Moreover it foams when heated. You may look for old books in regard tube manufacturing or use neutral high temp RTV.