Valve in a valve?

[pwdrive]

Sounds like a lot of faffing about to me but if that's what's wanted then good luck. Interesting engineering exercise though.

My solution would be to fit a B9A or B7G valve onto the old valve base then plonk an octal size metal screen over the lot.

Lawrence.

[boater sam]

We used to make sailing ships with glass strands and yes they had to be annealed after every few bits of the rigging was welded on else they cracked. I can't remember the temperature, it was not very high. Left cooking overnight.
Re-working CRTs was simpler, the neck extension and gun button was annealed on the lathe after welding, we never annealed cones and faceplates. The bake out during pumping was very hot, perhaps that helped with stress relieving as well. Have trouble remembering these details, I was 17 at the time and that was a long time ago.

[Cleggy]

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.T

Doesn't need to be WD40, any liquid will do and most glassblowers use spit (i.e. they just touch it with the tip of their tongue). The reason why it works has to do with the "Griffith Crack Theory" of materials, and 40 years ago, I might have been a bit more informative, but alas I will have to direct you to Google now if you need more info .

[Radio Fixer]

"Certainly really old windows are thicker at the bottom than the top."   I read somewhere that this just a myth but I don't have an old Victorian window glass to measure

Gary

[Ed_Dinning]

Hi Gents, it may be possible to hide an acorn valve in the base, a Russian rod valve of some of the small hearing aid valves. Versions of these valves were developed during the war for use in 3" AA shells. I have used tricks like this on 2V battery sets with the valve soldered onto the underside of the valvebase.

Ed

[Kalee20]

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.

It's more complex than that! Room temperature glass doesn't flow - if it did, the annealing operation would be unnecessary as stresses would just disappear themselves.

Old lenses and mirrors in telescopes and cameras don't flow out of shape making the equipment useless.

Old windows may well be thicker at the bottom than the top, but before the float glass process, making sheets of glass involved spinning a molten blob of the stuff, and it didn't give a uniform thickness. So when cut up for windows, the thicker region was put at the bottom - well, you would, wouldn't you?

[boater sam]

Before the float glass process there was the cylinder glass where molten glass was pulled vertically from the melt on a cylindrical former. It was then slit and opened flat to form sheet glass, hence the wavey old windows. And the early curved ones.

The spinning method is much earlier still, that's why window panes were very small, eg. georgian.   The poorer folk found glass too expensive so they bought the middle of the "spin" where the punty was hence the "bull's eye" panes.
 
I don't believe it flows either, as I said, I was told. I don't believe in lots of things that other people do, but that's the tale. Maybe its a tall one too!

I  do know that skilled glass workers make it look easy, I watched a guy making bowl drinks glasses with twisted colours in the stems, he made 12, all the same pattern and all the same size! And that was in quartz which is a pig to work because of the temperatures needed.

We shall see how it goes, certainly created a bit of interest though, has it not?

[Radio Fixer]

Thanks Kalee for killing the myth and explaining why.

Went to Venice a few years ago and to Murano to see the glass made there.  Fantastic pieces at huge prices but I expect the work is long and breakage high.  Best was a flat sided bowl, like an open shopping basket about 12 to 15 inches long, in a white cloudy glass.  It had then been overlaid with chocolate brown ribs of glass, say 6 mm across that were at an angle to the bowl and spaced about 25mm apart.  Then the handle was made as a twisted rope of the white and brown glass.  Think it was E500 for cash !!

Gary