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Old 29th Nov 2017, 3:09 pm   #1
David Simpson
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Default Care of Rare Valves

A recent thread in "Hints & Tips" has prompted me to encourage folk to take extra care with rare valves. Plus the fact that a BVWS chum has recently asked me to test all his special 1920's valves, many NOS & Boxed. I've taken it on as a privilege. We're talking Marconi LS5's & the like ! I've tested two LS5's so far, successfully, and there is another three to do. Jesus - have you seen what horrendous prices are being asked on the internet. There are dozens of other early 1920's valves. The most rare & expensive ones I'll put in a dedicated box.

Regards, David

PS I'm just about to start on a 1921 Mullard 0/20. I dread to think how rare this Tx valve is ?
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Old 30th Nov 2017, 2:08 am   #2
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Default Re: Care of Rare Valves

Turning valves like a wine bottle:

Glass acts like a super cooled liquid or like toffee. Quite a few valves from the 1920's era have been damaged by storage on a shelf on their sides in a box for 60 to 80 years without being moved.

It especially effects the ones where they are globe shaped valves without an upper mica insulator from the top anode structure area in contact with the glass. I have a few where the anode assembly slowly fell down and the distortion of the structures also caused filament - grid shorts.

So ideally vulnerable valves to this effect should be stored vertically in the gravitational field, or be rotated 180 degrees every few years.
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Old 30th Nov 2017, 2:24 am   #3
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Default Re: Care of Rare Valves

I thought the idea of glass flowing over time was a myth that has been disproved. For instance there are many examples of Roman and Egyptian glass items that are thousands of years old and show no distortion whatsoever.

I may be remembering this wrongly.

Cheers,
Steve.
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Old 30th Nov 2017, 3:37 am   #4
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Default Re: Care of Rare Valves

It is an urban myth, usually?
It came about due to folk finding very old window glass that was thicker at the bottom than the top.
However, you have to realise how this really old glass was produced.
"Flat" glass was made by spinning to produce a disc that was then cut up. The poor people could buy the center parts ie. the 'bullseye' where the pintle was, cheaper than the outer parts.
Later glass was drawn up from the melt on a circular former to produce cylinders which were then slit lengthways and opened out whilst still plastic.
This produced the inevitable distortions, ripples, where the glass was different thicknesses.
Mechanically rolled glass is made usually in obscure and wired patterns due to the surface not being perfect unless polished afterwards, hence can have thickness variations too.
Now, think of the glazier faced with a pane of glass thicker at one end, of course he would tend to put the thick bit at the bottom of the pane to reduce the squeezing out of the putty.
Molten tin lehr "Float" produced true flat glass has been around for a long time, I have taken out thousands of pieces and never found one thicker at the bottom.
But if you are convinced that the super cooled liquid continues to flow in a period of only 100 years, so be it, who am I to argue, I'm not that old, yet.
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Old 30th Nov 2017, 3:41 am   #5
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Default Re: Care of Rare Valves

Quote:
Originally Posted by fetteler View Post
I thought the idea of glass flowing over time was a myth that has been disproved.
I think you are right about this, generally a myth about window panes thickening up at the bottom etc.

However in the case of the valves with bent over electrode structures it is only movement of the glass support where the pins/wires enter the globe that could explain it. The outer globe though never shows any evidence of distortion or deformation.

One other explanation offered for the badly tilted over anode structures was that they were manufactured this way, but that is harder to believe, especially when some have moved far enough to short the electrode structures together.

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Old 30th Nov 2017, 3:59 am   #6
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Default Re: Care of Rare Valves

I did say"usually"! to cover my butt.
I can't account for this distortion either but I have seen loads of badly made valves with bent pinches and always assumed that it was poor manufacture, possibly post assembly annealing.
Can anyone prove us wrong?
I have seen power valves and rectifiers that have become plastic due to excessive heat and distorted that way.
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Old 30th Nov 2017, 4:57 am   #7
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I have seen power valves and rectifiers that have become plastic due to excessive heat and distorted that way.
Yes I have seen that too.

In general though I agree that calling glass a super cooled liquid or thinking of it that way is wrong. Probably best called an amorphous solid.

So the question remains, if you have an 80 year or more old globe tube, but not a power tube that been heated, where the electrode structure has no upper mica support to the bulb, and it is badly bent over and the filament and grid are shorted or near shorted...how did it get that way?

If we propose it was manufactured that way, is that likely ?

One thing I have noticed about components from this era, there appears to have been a lot of pride in the appearance of them and the QC was reasonable. Everything was well done, right down to elaborate and colorful packaging. I don't think a customer would have accepted and paid for a valve in this obviously unusual condition. If it was seen at the factory it would have likely failed testing and been discarded. So I struggle to think this is likely.

(I'll attach a photo of one tonight).

So if the tube was "normal" when new, did it really slowly change over 80 years ? and if it did, was it gravitational force that caused it and if it was, did the glass support system move or not ?

One thing about the way the glass supports were done, they are actually very thin (a small fraction of typical window glass thickness) near the point where the support assembly joins the bulb. A very small change here would result in a larger position change much further away near the top of the anode assembly. But one thing here, it appears also that the relative positions of the wires crimped into the support assembly, which set the inter-electrode spacings, have moved (or were incorrectly placed initially) as well as the overall position of the support moving.

So I'm not really 100% convinced either way.
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Old 30th Nov 2017, 5:13 am   #8
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Default Re: Care of Rare Valves

A topic for open discussion. The Uri Geller syndrome? If glass slumping is a phenomenon, safe storage in the Space Station?

Never seen a CRT with this effect despite being horizontal and heavy with weighty scan coils and magnets on the neck. Odd?

As for pride of work, I have had many octal valves, mainly of US manufacture, where the base cap has been fitted cack handed. And they are not loose ones that have been reglued either.
I suppose when production was king and valves were coming to an end anything that could be sold would of been. The war production too may have lead to an over hasty production schedule in some areas.
I also have a few misshapen B9A valves and they were all machine produced.
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Old 30th Nov 2017, 5:50 am   #9
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Default Re: Care of Rare Valves

I think glass flowing is a myth. I have used (although don't own) an astronomical refracting telescope with an objective lens over 150 years old. I have (and use) camera lenses of half that age. The optical performance would be ruined if the glass had flowed at all. And the effects noticed in 80 year old valves would seem to be a lot larger than the amount of flow to ruin a lens of a similar age.
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Old 30th Nov 2017, 6:00 am   #10
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Default Re: Care of Rare Valves

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And the effects noticed in 80 year old valves would seem to be a lot larger than the amount of flow to ruin a lens of a similar age.
That is a very good point it wouldn't take much to totally degrade the optical performance of a lens.
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Old 30th Nov 2017, 9:24 am   #11
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Default Re: Care of Rare Valves

I've attached photos of a CX371 (aka UX171) with a slumped over electrode structure. I have an extensive collection of these and the typical UX201A type tubes.

One problem, on the bulk of them, I cannot see inside to inspect the position of the electrode structures because they mostly have a getter that has silvered the entire bulb.

Certainly I have never seen this issue in ST or shoulder shaped tubes, or any octal or smaller tubes. Mostly they have a top mica support, but of course that would also have had to center the electrode structure in the bulb at the time of manufacture.

In this particular tube (still under vacuum) the positions of the electrode support structures are also a bit disorganized and the physical relation of the filament support is such that the filament and grid just in contact. Like this from new, I wonder. The tube would be about 1924 to 1927 vintage I would guess.
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Old 30th Nov 2017, 9:44 am   #12
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Default Re: Care of Rare Valves

Is the effect reversible? Could you positon the valve so that gravity tends to pull the electrode back to the correct position and see what happens?

It would be a very long experiment of course!
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Old 30th Nov 2017, 9:54 am   #13
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Default Re: Care of Rare Valves

Thinking about it, I have often seen this but never considered that it was anything other than a hand assembly error. Do they always lean in the same plane, not sideways or twisted?
Ignoring the obvious valves where the electrode assembly is deliberately set at a steep angle in the envelope, like PX4 etc, would they worry about this when hand making valves?
Could it be simply the annealing process whilst the valve was pumped that caused the assembly to move, being the last hot operation, and they considered that it was not important to the operation of the valve?
Later valves all had mica top supports, perhaps this is why. The change to bulb shape is vital to fitting a top support, in the early balloon shape it is not possible. They had to have a rigid support frame for the electrodes.
Also the heavy over gettering often completely silvered the bulb, hiding the misplaced assemblies, deliberate?
I don't suppose we can find anyone now that was involved with this early production, they would be unlikely to recall it anyway!
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Old 30th Nov 2017, 10:10 am   #14
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Default Re: Care of Rare Valves

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Is the effect reversible?
It would be a very long experiment of course!
Yes, I'm afraid I don't have time to find out!
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Old 30th Nov 2017, 11:31 am   #15
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Default Re: Care of Rare Valves

Quote:
Originally Posted by Argus25 View Post
I've attached photos of a CX371 (aka UX171) with a slumped over electrode structure. I have an extensive collection of these and the typical UX201A type tubes.
Are they all Cunningham tubes? Considering the relationship between RCA and E. T. Cunningham could it be that RCA selected the 'imperfect' examples of their production for supply to Cunningham? Just a thought!
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Old 30th Nov 2017, 12:41 pm   #16
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Default Re: Care of Rare Valves

I consider it possible that very old valves with mis aligned electrodes might have been made like that.
Such "B grade" valves might have been sold at reduced prices to hobbyists, experimenters, researchers, or to staff at the works.
Such valves might be more likely to have survived 80 years or more in "great granddads workshop" than a heavily used perfect example.

Or they might have been dropped ! under certain conditions the forces thus resulting could bend internal metal parts out of shape but leave the envelope intact.
I have observed electric lamps that have been dropped and the filament thereby displaced. Such lamps often work fine for say room lighting, but would perform very poorly in a sophisticate optical system.

In the case of very early valves, design and manufacture were less well understood than in later years, and more empirical than scientific.
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Old 30th Nov 2017, 1:48 pm   #17
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Default Re: Care of Rare Valves

This question of "flowing glass" always sparks debate. In the case of valves, if the glass flows then surely we would see the envelopes collapsing (bulging inwards) due to atmospheric pressure, irrespective of orientation, during storage? However, the question of "best practice" for storing valves is a good one.

To the best of my knowledge, there is no one on the forum who is a "professional" conservationist - I'm thinking of someone who works in one of the major museums. I'd guess that in the Science Museum, for example, there must be a department who have a very high degree of expertise, built up over decades and shared with other museums across the world, who deal with many of the kinds of issues that we discuss on the forum. The question of cleaning vintage objects springs to mind. Perhaps we should put out feelers? Just occasionally, I'd guess they could learn from us.

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Old 30th Nov 2017, 2:12 pm   #18
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Default Re: Care of Rare Valves

Quote:
Originally Posted by Boater Sam View Post
It is an urban myth, usually?
It came about due to folk finding very old window glass that was thicker at the bottom than the top.
However, you have to realise how this really old glass was produced.
"Flat" glass was made by spinning to produce a disc that was then cut up. The poor people could buy the center parts ie. the 'bullseye' where the pintle was, cheaper than the outer parts.
Later glass was drawn up from the melt on a circular former to produce cylinders which were then slit lengthways and opened out whilst still plastic.
This produced the inevitable distortions, ripples, where the glass was different thicknesses.
Mechanically rolled glass is made usually in obscure and wired patterns due to the surface not being perfect unless polished afterwards, hence can have thickness variations too.
Now, think of the glazier faced with a pane of glass thicker at one end, of course he would tend to put the thick bit at the bottom of the pane to reduce the squeezing out of the putty.
Molten tin lehr "Float" produced true flat glass has been around for a long time, I have taken out thousands of pieces and never found one thicker at the bottom.
But if you are convinced that the super cooled liquid continues to flow in a period of only 100 years, so be it, who am I to argue, I'm not that old, yet.
Very good post, however in between the spinning a gob of glass on a metal rod to obtain a circle of glass, and the method of feeding it between rollers. There was another method, which was the one that gave the roller idea. a "gob" of molten glass was attached to a blowpipe and blown, it was then swung until it stretched, and the blowing continued, eventually you ended up with a cylinder about 3 feet long, chop off the ends, slit down the middle and place back in the lehr, to anneal and flatten.
It's funny but most of my family were involved with the local glassworks, my paternal grandmother polished glass for mirrors, her husband (my grandfather) worked in the packing warehouse. my father was a plumber in the same company, and my mother, well she delivered parts for a hydraulic company, quite often to the glassworks!
I became an apprentice electrician, in a steelworks instead of taking up the offer of a plumbing apprenticeship with the glass firm. I used to joke that I was the only one who had escaped the family tradition, however years later I'd grown fed up with the electrics, and for a while became a dog handler. Imagine my surprise when one day I answered an advert for someone to run the dog section at a local firm, I got the job, then found out who's dog section I'd be in charge of, yes you guessed it, the glassworks.
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Old 30th Nov 2017, 3:44 pm   #19
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Default Re: Care of Rare Valves

OFF TOPIC ?
Very interesting as it is - the aging process of the molecular structure of glass - I was hoping that folk would let us all know their methods of packaging & storing of rare valuable valves. eg. Bubble-wrap versus corrugated cardboard, heavy duty cardboard boxes versus B&Q type cheapo plastic lidded boxes, etc.
Argus 25's point about vertical storage of valves is well worth noting. I also note that some 1920' & 30's valve boxes have internal cardboard formers which are shaped to take the base & its pins at the bottom, whilst others are designed to take valve's heads & top-cap downwards. But then, I've a 1928 Scott-Taggart ST400 TRF which had its SG valve mounted horizontal.

Regards, David
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Old 30th Nov 2017, 5:21 pm   #20
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Default Re: Care of Rare Valves

I reckon the bend in the electrode structure is due to impact. There is a very flexible point as the contacts to the electrodes exit the glass base of the valve and if the valve is dropped (in its packaging of course!) then depending on the direction of the impact the inertia of the electrode is enough to bend the support. The electrodes in the picture are leaning over at a greater angle than the glass stub they are attached to... Always go for the simple explanation!

Cheers,
Steve.
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