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Old 29th Apr 2012, 1:30 pm   #1
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Default Taking bases off valves, safely?

Faced with a miserable little collection of blown up octal valves, I wonder if there is any reasonably safe way to remove the bases from the bulbs, for possible use as adaptors etc.

To make things a bit harder for me, the valves concerned are low power battery types (Mullard DK32 etc.), which have clearly never run very hot, and at present seem very firmly fitted together.

For instance, could anyone suggest solvents which could attack the cement used tobsecure the bulbs without destroying the base insulation, ( Bakelite? other phenolic ? Or perhaps a hard rubber / ebonite ?)

My own guess would be methylated spirits - but perhaps something stronger would be needed to undo a marriage of some sixty years

Last edited by Adjuster; 29th Apr 2012 at 1:31 pm. Reason: To add a missing word.
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Old 29th Apr 2012, 1:34 pm   #2
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Default Re: Taking bases off valves, safely?

Doing a search of this forum (see google search at top of page) there are suggestions that Acetone is one chemical that softens the cement that secures the valve base to the glass. There is a link on a solution to the problem here:-

https://www.vintage-radio.net/forum/...ing+valve+base

Last edited by wave solder; 29th Apr 2012 at 1:39 pm. Reason: added link
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Old 29th Apr 2012, 1:40 pm   #3
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Default Re: Taking bases off valves, safely?

Sounds like you also need 4 B7G sockets and a set of Dx9x valves to go with them........
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Old 29th Apr 2012, 1:41 pm   #4
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Default Re: Taking bases off valves, safely?

It's often possible to break the adhesive by careful manipulation. If that doesn't work I would just smash the glass over a cardboard box or other container, taking great care of course.
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Old 29th Apr 2012, 3:05 pm   #5
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Default Re: Taking bases off valves, safely?

Quote:
Originally Posted by Herald1360 View Post
Sounds like you also need 4 B7G sockets and a set of Dx9x valves to go with them........
That would be a bit brave of me, I think, but might just be tempted to try it with the output valve. I have in fact got some B7G sockets just in case. Even just doing the last valve would presumably need some bias change to get the anode current somewhere reasonable - don't want to cook up my nice NOS DL94 or whatever. As for the anode loading, well beggars can't be choosers.

The mixer and IF will be octal anyhow, but don't know about the DAC32, the equivalent newer series valves are diode - pentodes! A good look at the schematic would be in order before doing anything too drastic, after all, I have no idea what other faults may lurk in the set before thinking of modding it.

Never take a description of something being untested, especially sight unseen - the set in question arrived beautifully packed, but still inside it were the crocodile jumper leads which had most likely been used to fry it!
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Old 29th Apr 2012, 4:12 pm   #6
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Default Re: Taking bases off valves, safely?

Quote:
Originally Posted by Adjuster View Post
Never take a description of something being untested, especially sight unseen - the set in question arrived beautifully packed, but still inside it were the crocodile jumper leads which had most likely been used to fry it!
Be especially wary if the vendor has "tested" and "untested" piles ..... yes, I have actually seen this at a radio rally once.
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Old 29th Apr 2012, 5:36 pm   #7
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Default Re: Taking bases off valves, safely?

I recently wrapped a faulty octal valve in newspaper and tapped it with a hammer to break the exposed glass.

By gripping the remaining glass inside the base with a pliers (while wearing eye protection, tough gloves and then wrapping a cloth around the base to stop flying glass) I twisted and crushed it.

The adhesive could then be carefully scraped out.

That valve was already cracked. It was a messy job and despite my precautions glass fragments managed to escape.

I will try solvents the next time!
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Old 29th Apr 2012, 6:22 pm   #8
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Default Re: Taking bases off valves, safely?

Thanks for the suggestions. I had hoped not to resort to a hammer, but no doubt that's what I will do if all else fails. Acetone sounds worth a go first though, perhaps in sealed up in something like a small jar to allow it to penetrate for a while.

The main target for these might be another old set in much worse condition to be attacked later on, rather than experimenting on this present one. Maybe it's a bit daft, but somehow I wanted to salvage something from the Phantom Fiddler's efforts.
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Old 29th Apr 2012, 6:37 pm   #9
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Default Re: Taking bases off valves, safely?

the "glue" tends to be a mixture of shellac and wood flour and is normally softened by meths
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Old 29th Apr 2012, 8:27 pm   #10
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Default Re: Taking bases off valves, safely?

Thanks again - I wonder if I might have had some apart by now if I had been soaking them in spirits for the time of this discussion!

Enough chatter then, off to the shed to see if that bottle has any left in it..
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Old 29th Apr 2012, 9:39 pm   #11
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Default Re: Taking bases off valves, safely?

I've found that if you can find a convenient jar into which the octal fits and can be filled with enough meths to easily cover the base, if you leave them overnight and then try going round with a hot iron and tweaking, the valve comes off easily. The shellac and woodflour cement is reduced to soft sludge.

If the jar has a screw top it will do for many more candidates.

If you only want the base, this is still the best way to go because you can clean out the cement with a bit of bogroll and have a clean base.

If you decide to go the hammer route, be sure to wear full protective clothiing, but you''re still likely to have the cement to deal with as well as the hazards of broken glass.

Pete
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Old 29th Apr 2012, 11:13 pm   #12
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Default Re: Taking bases off valves, safely?

I only had to separate a base on one occasion and as an experiment I boiled the valve in a saucepan of water for 20 minutes, and that did the trick. Perhaps that valve had weak adhesive and this method would not work on all bases.
John.
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