Having collected large numbers of valves over the years to use in Radio’s and Television’s.
I have a number of early Radio valves which have a conductive coating on them, you know the painted areas on the glass envelope for shielding the valve from interference from other components nearby and the valves are normally covered either in red, grey or even gold colour.
But I have some vacuum tubes which the valve’s paint have started to flake of the glass and would like to stop more coming off the glass, either looking to protect the existing coating or would like to try spray paint the missing areas with some conductive coating and even try to match the colour as well, a big asked I know, but I would give anything a try.
Perhaps the only way is to remove all the flaking coating off and start a fresh with some new coating.
Has anyone been able to do this successfully and would be interested in what methods you have tried and have worked; I would have to masked the area not needed to be coated, spray painting is possibly the only way to get a smooth finish on the surface.
Was thinking of a small art airbrush, spray pen kit. Would conductive coating work with a airbrush? what do you think?
Keith
@keithr There are paints based on nickel silver sold for screening purposes, but they are not particularly cheap. I used to use Electrolube NSC (later NSCP) but it doesn't seem to be available any more.
Hi Cathovisor
Thank you for your help. I will do some investigating into nickel silver paint and see whats available. I got something to start with.
This has been discussed elsewhere several times. I don't think that there has been a conclusive answer, you cannot guarantee that a metal based paint will be conductive when it has been applied and dried.
The silver loaded paint is fine but terribly expensive to coat a valve with.
Aluminium paint does not work.
This has been discussed elsewhere several times. I don't think that there has been a conclusive answer, you cannot guarantee that a metal based paint will be conductive when it has been applied and dried.
Well, this stuff should be fine: https://mgchemicals.com/products/conductive-paint/conductive-acrylic-paints/nickel-conductive-paint/
But, at GBP63 for a 340ml aerosol of the silver/copper version (it may be cheaper elsewhere)...
Hi Boater Sam
It's fair point, I have checked the cost for a small bottle of Electrolube silver conductive lacquer for electronics, about £20 and the other thing I do know, is to take in consideration that the paint will have a short shelf life once opened. Would need to do a number of valves at the sametime to make it worth well.
Keith
Thanks Cathovisor
I will look into Super Shield Nickel Conductive Coating and to see if it's cheaper, I need to check on what's the shelf life is once opened.
Keith
Can't say if this will work as I only have experience of welding but try a car shop, you can buy weld through primer and there is a copper coloured one too.
I will look into this as well thanks.
I haven't tried it, but one can purchase "Guitar screening paint", intended to be painted around where the pickup is mounted to reduce hum. I suspect that its active component, described as graphite, doesn't provide as low a resistance as the metallic types but it's cheap enough to be worth trying. The main problem with any screening paint may be getting it to adhere reliably to glass- back in the day, North American manufacturers seemed to be better at achieving this than British ones. It's not unusual to find pre-war British valves with the coating hanging loosely around the envelope like a crumbly grey petticoat! It may be that those manufacturers that managed to get the coating to adhere reliably roughened the glass surface with something like hydrofluoric acid that would make the H + S folk turn pale and fall over nowadays.
Hi turretslug
As you said getting it to adhere reliably to glass is going be one of the problems, but looking at mgchemicals 2-part conductive epoxy paint It states that it is corrosion and chemically resistant, also states it adheres very strongly to metal, glass, ceramics, and most plastics. Nickel epoxy paint can be used to provide galvanic corrosion resistance between mated surfaces. It can also provide RFI shielding or grounding in harsh environments.
It's one of the options but it is going be too expensive to buy, maybe I could find it cheaper elsewhere if I look into it further.
As I said, it's also the shelf life once it opened, how long before it drys up completely.
My vacuum tubes with the coating, some of the paint are hanging loosely and or missing some around the envelope, the valves themselves are working fine. I will look into the Guitar screening paint you have said and see if it would adhere to glass. A good idea.
Keith
Nickel Conductive Paint used to be relatively easy to obtain, even Maplin sold it. Then, before I could buy any it became very difficult to find and if you did, expensive! Although I’ve never used it I really wish I could have bought some. Did it go the way of Carbon Tet because it became classed as super dangerous? Indeed does any UK supplier have any?
I have many valves with deteriorating coating so any solution would be good. I’ll look into the guitar paint.
All I have is my ancient bottle of Elecolit 340 conductive silver paint. At 3gm it not going to cover much even if it is still usuable.
Peter
The tiny bottle…
EF39's are supposed to be well known for peeling paint and I have a couple that are practically devoid of any. If I plug them into a radio it will motorboat and fail to work. I used to have a little bottle of electrically conductive silver paint like that in the post above. Think I purchased it for a repair of something years back and it was also very expensive back then. I might even still have it somewhere. It wasn't even half full when purchased brand new, so there is not a lot of paint to go round for painting on valves, just for touching up maybe. The paint might be worth using on some esoteric and rare valve to rescue it, but for sure not on an EF39! The valve will have a small thin wire protruding from the top of the base that connects the coating. At least it does on the EF39. This wire must still make contact with whatever substitute is used. There was a suggestion to wrap some foil around it, which I carefully did being careful not to let it touch the cap at the top. The contact with the screen wire at the bottom was not that reliable though. I haven't found a good alternative yet. Will keep an eye on this thread out of interest. I am curious whether that Guitar shielding paint or something like Rustins G-Shield (graphite) would work.
