Valve in a valve?

[boater sam]

I have spent many happy hours gutting and re-stuffing capacitors, some think it a bit anal but I prefer the look.

The thought occurred to me in an idle moment lying in the sun that the same could be done to valves.
It is easy enough to get the base cap off B4/5, B7, Octal etc valves, heck, they fall off on their own. So could a small valve be planted inside the old envelope and the base refitted?

B9A and B7A valves could be used, the function of most old valves is duplicated in more modern types, the pins could be extended into the base cap with wire and the whole re-assembled to look like the original.

I need to find a way of getting into the bottom of the glass envelope without breaking it, take out the stem and electrode assembly to make sufficient space for the substitute.

A quick spray inside with chrome paint could replace the getter flash and hide the ersatsz valve. Heat may be a problem, there would be no convection cooling only radiation to the original glass.

Anyone tried it before? Am I getting carried away, daydreaming?

It would resolve the availability problem of valves like EBL31, sub in a pentode, say EL84, and 2 silicon diodes hidden in the base.

Sam.

[Pat Pending]

I think you would have to let the air in then score 'n' tap instead of trying to do it all in one operation. Be careful with the chemicals though. Regards. Andy.

[Radio Fixer]

Some while ago Peter Kayne? of the BVWS made some very convincing early screen grid valves. These were the type that are double ended and he used a polished ali tube between two rescued bases. Suitably paper labelled up they looked good from the pictures. He added components to get similar characteristics as the original from the B7G types he choose.

Gary

[boater sam]

I think it would be possible to grind the lower edge away, gently, then tap to fracture. Would there be any chemicals to cause a hazard?
I can only think of the cathode coating, is it likely to be Thorium?
Used to cut CRT neck tubing with a hot wire but the shape of the pinch base may make that impractical if I need to leave enough of the lower bulb to glue the base back on.
Its been a good few years since I did any precision glass work!

[Nick]

The glass becomes very brittle with age & heat.

Here's a tip - score all the way round the valve, cleanly in one joined up line - do so as close to the biscuit (the bit with the wire/pin feedthroughs) as possible. Then wipe the scored groove with WD40 and with the valve wrapped up in something protective and wearing eye protection & gloves, tap gently around the score with the end of a decent screwdriver. The "hot wire" (W or NiCh) technique is also very good for tubular work - lots of videos about this online.

The WD40 (or paraffin)  is a trick given me by a hot glass worker (no innuendo please!) - for some reason the breaks are always cleaner, but old glass is always more difficult to work with than new - I also do neon sign work, and old glass is not good stuff to handle - new is easy to snap cleanly.

I would certainly "gas" the valve by breaking the nipple before attempting to decapitate it.

See: http://www.teralab.co.uk/Glass_Blowing/H..._Page1.htm

[Radio Fixer]

I read that glass retains a lot of the stress of manufacture and that's why it flies when broken. Maybe those stresses become more brittle with age and UV. Certainly trying to cut old window glass never worked even with a diamond scribe.

Gary

[boater sam]

I was told years ago that glass is a supercooled liquid, whatever that is, and that it continues to move. Certainly really old windows are thicker at the bottom than the top. Defies logic but there you go.

CRTs are mostly lead glass, I don't know about valves, but most blown glass is lead, cast glass can be crystal as I understand it.

Straight cutting old window glass is difficult because the surface is contaminated. We used to polish the surface with an abrasive and then it cuts much like new glass.

I have re-necked lots of old CRTs and had no particular problems but using many thousands of pounds of glass lathe does make life simple!
The re-gunning trade did not seem to have a problem, and some of the tubes they worked with must of had many years of use.

Will have a go when I get back, something else to do, retirement is so hectic.

[Yorkie]

Anyone tried it before? Am I getting carried away, daydreaming?

It would resolve the availability problem of valves like EBL31, sub in a pentode, say EL84, and 2 silicon diodes hidden in the base.

Sam.

The problem with EBL31 valves, is that all of those sold by the main UK valve dealers aren't EBL31s at all - they're EBL1's which have a side contact base and a 3/8" top cap, whereas  the EBL31 has a 1/4" top cap and a short octal base. The converted EBL1 valves simply have an octal base glued over the side-contact  base, which - if there's space to accommodate the taller converted valve isn't a problem, but given that EBL31s are used mostly in Ekco A22s,  the converted valves are useless. They can be converted properly and I've converted several NOS EBL1s by carefully cutting the side contact base and fitting a cut down octal base cross-wired to the valve, then I've removed the3/8"  top cap and fitted a 1/4" one. It's a tricky task which calls for a steady hand using a Dremel type drill with a cutting disc. I wrote up my experiences in a BVWS Bulletin article.

Before I found EBL1s to convert, as a temporary measure I made an adaptor using an EL84 valve, and two germanium diodes hidden in the octal valve-base, with a 'top cap' mounted on the side of the valve-base  That has the merit that there is no re-wiring of the valve-holder on the set.  Of course, it does look rather comical, but it was functional for some months till I got my hands on some EBL1s to convert properly. EBL1s don't seems as rare as genuine EBL31s, and not as costly. (I bought two new in box at £10.00 each from Golborne, and another three from the NVCF from a dealer who said "these can be converted to EBL1s you know - some bloke wrote an article in the Bulletin about converting them".  I didn't let on, feigned disinterest but idly said 'really - how much for all three?", and he said "£15.00".  So, in effect, with a bit of effort and skill, five potential EBL31s for the price of one useless 'Big Bertha'.

Can't comment on the 'valve in a valve' idea - If Gerry Wells had still be around and anyone had said to him 'It would be impossible to do such a thing' , he'd soon take the task in hand! 

I've attached a few pics. I originally thought there were two types of EBL31s - small and tall. I spoke to Gerry Horrox who soon put me right on that score - he said "yes, there are two types - genuine and fake".

Hope that's of interest, albeit rather off topic from the 'valve in a valve' idea.

You've set yourself a challenge Sam - go for it!

(Plenty of space in a valve-base to fit a couple of silicon rectifier diodes in a hard to find expensive rectifier valve).

[Nick]

I read that glass retains a lot of the stress of manufacture and that's why it flies when broken.  Maybe those stresses become more brittle with age and UV.  Certainly trying to cut old window glass never worked even with a diamond scribe.

Glass is a complex & subtle material, however after being hot-worked, it's annealed - see https://en.wikipedia.org/wiki/Annealing_(glass)

The videos I've seen of the Blackburn works valve production lines certainly show an annealing process as part of the production line (*), so internal stress should not be an issue, even for early valves as this is a well known problem.

(*) there are normally several annealing phases, one after each major hot-glass procedure.

[boater sam]

Hi, David,
I was aware of the EBL1 fudge, originally done by the valve makers I believe. That's one reason I thought of doing the valve re-stuff on EBL31s initially, they are going for daft money and it would be possible to bring the height down to fit A22s. But then I would have to find some duffers to alter.

I've done rectifiers by just putting the diode/s in the base and refitting the glassware, cutting the anode and cathode leads off inside, so that they still glow!

I also need to consider how to get the top cap connections on inside the envelope.  Springs! Onto the remains inside.