Loose valve bases
Back in the mists of time when I had a Marconi comms receiver a number of the valves were loose on their (octal) bases.
At the time I used model aeroplane cement. Is this of a different make to that of Superglue. Araldite goes soft with heat, but there are various sorts. What is the safest option to secure a valve that is loose on its base? |
Re: Loose valve bases
Hi Neil, I think the general opinion here is that two part epoxy type adhesives are best for this job, I tend to use the quick setting variety and have had no problems. Superglue is definately not reccommended! see here :) :-
https://www.vintage-radio.net/forum/...read.php?t=400 Regards, Mick. |
Re: Loose valve bases
Hi Neil,
For anything that is NOT a power bottle (output, or rectifier valve) superglue is ok, but in moderation - a few spots around the base, just to hold it. for everything else, evostik - the smelly one is very good, not the wood glue..... Cheers Sean |
Re: Loose valve bases
Hi Neil
I read somewhere, possibly on this forum, that you can use acetone dripped down between the base & the glass. The idea is that it dissolves what is left of the original glue, then evaporates leaving the original glue holding the base on. I've never tried it but its worth a go. Use pure acetone, not nail varnish remover as that often contains oils & skin treatment stuff. Joe |
Re: Loose valve bases
I always use Araldite for this.
Mix up a small quantity and use a match stick or end of a cable tie to "grout" between the glass and base. It seems to stand the heat OK, although I would recommend the stuff which takes 24 hours to harden as this seems to be the most heat resistant. I have seen Araldite used to mend aluminium castings on motorbike engines and car radiators. Good luck with whatever you use, and that's a few more valves rescued!:) |
Re: Loose valve bases
Oh, another idea, as used by the MOD - Adhesive lined heatshrink - great stuff, and an almost permanent repair!
Cheers Sean |
Re: Loose valve bases
Neil, do you mean the plastic type of model aircraft kit glue? This is polystyrene cement and actually works by "melting" the moulded plastic parts together. In my experience it isn't much use on other materials.
Biggles. |
Re: Loose valve bases
Well, it was a very long time ago, about 1984-5. I had a tube of this stuff around and I remember it was for glueing plastic. I used to use it to glue the plastic adapters into the centres of 45 rpm singles. It stabalised all the valves but they weren't rectifiers or audio output types, mixer and IF strip at a guess. Audio o/p was a 6V6GT.
I have some Araldite but it is the 'rapid' sort. I tried it to effect a bodge on some damaged threads on a Enfield motorcycle I owned eight years ago. Under heat it softened to a chewing gum consistency. A bit wasteful buying a whole tube to do one single valve, but how does one recognise the 'good' Araldite? |
Re: Loose valve bases
Have used heatshrink too, it works well.
The rapid stuff is no good for more "demanding" applications(such as engines!!!). The 24 hour stuff is the best. I think the variants come in different coloured packets. There have to be more uses than just one valve? |
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Nick. |
Re: Loose valve bases
Quite right Nick. I only have blue in that size!
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Re: Loose valve bases
I have seen it at Radio Rallies up to 6" diameter, and you only need hair drier heat to shrink it down, so, not too risky..... I wouldnt try it on immensley rare output bottles though - just in case;)
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Re: Loose valve bases
From what I know Araldite is not suitable for fixing glass envelopes to valve bases. A common way to soften hardened Araldite is to heat it to around 120ºC. At higher temperatures it no longer solidifies when cooled down again, but starts to break down chemically. By then it looks really ugly as the adhesive starts to foam up.
The highest operating temperature I found was 85ºC (type 2014), which is of course way too low for valve repairs. Hope this helps a bit. Frank N. |
Re: Loose valve bases
I've seen the heat shrink on a couple of Zaerix valves. I didn't realise it was a MOD thing, it looked like a Zaerix special.
I've used PVC tape to fix loose envelopes to the base of octals and I've had no problems. I've also got a rectifier which has been lashed up with masking tape and a few valves with old fashioned black tape. Taped up octals have never caused me any problems. You don't want the envelope loose, but on the other hand, if you can possibly help it, you don't want to extract a valve by pulling the envelope. I've used Araldite to re-attach top caps and that's always worked. I can see that the tape wouldn't do for valves prominently on display in an audio amplifier. Pete. |
Re: Loose valve bases
I've used Evostick for years with no problem. You can apply it with a matchstick and just leave the valve for twelve hours or so. While it is still in liquid form you can wipe away any excess and the end result is a really neat repair.
Rich. |
Re: Loose valve bases
I normally use Araldite, but I needed an invisible repair for my, glass backed, RAP 646.
I took the idea in post #4 (using acetone to reactivate the adhesive) one step further and used clear nail varnish, heavily painted around the joins. When dry I cleaned the surplus with nail varnish remover (what else! :-D) The radio has been on for 1 hour, cooled down and the bases are still stuck solid... Oh, it stuck the top cap connectors too :D David |
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stores that had been repaired using this method. Excellent repair job. Ian |
Re: Loose valve bases
While on this topic;how do I save a couple of valves with broken Top connections?Both have lost the wire that protrudes through the glass?They are 6k7 and 6A8G types from 1949 IMMSMW.They were working fine until tops fell off.
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I suppose there's nothing to lose, but I wouldn't bother for relatively common valves like these. Paul |
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