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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 11th Jul 2018, 6:00 pm   #1
G1RAO keith
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Default Valve base detached from glass part.

Hi
Has any one managed to re glue a valve base ,the old brown glue is no longer available I expect,I need to glue one on a valve that is likely to get quite hot and I thought something like araldite may soften.keith
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Old 11th Jul 2018, 6:23 pm   #2
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Default Re: Valve bases

If its only loose I use PVA.
If its really off, fine wood dust and PVA.
Originally they used shellac and wood dust.
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Old 11th Jul 2018, 6:47 pm   #3
G1RAO keith
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Default Re: Valve bases

Hi
thanks for the reply.the base is completely off I took it off because the heater connection was
o/c at the valve pin plus it was loose anyway it's a B4base so not a problem sticking it back ,I will try that with PVA and saw dust.keith
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Old 11th Jul 2018, 7:15 pm   #4
Mr Moose
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Default Re: Valve bases

Hello,
Shellac disolves in alcohol so I have stuck a couple of older valves back to their bases by using a fine brush to get methylated spirits between the base and the, glass leaving it for a short while to soften the shellac, then repeat several times, then a final dose and push together and hold for a while till the meths evaporates.
obviously this will only work where shellac has been used originally.
Yours,Richard
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Old 11th Jul 2018, 8:38 pm   #5
G6Tanuki
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Default Re: Valve bases

A short fat bit of adhesive-lined heatshrink sleeving is my go-to for this; OK it doesn't work on 'power' valves like 807s where the glass bottle's expected to be running at well above the softening point of heatshrink-sleeve glue, but for signal-level valves it works just fine.

And it has history: I've got several Air-Ministry VR100/VR101 valves here which had the heatshrink-treatment back in the 1960s and are still happily working.
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Old 12th Jul 2018, 9:54 am   #6
David G4EBT
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Default Re: Valve bases

As has been said, the original 'cement' used to secure bases and top caps was a mixture of shellac and wood flour. It can be softened and removed by immersion in methylated spirits (known outside the UK as 'de-natured alcohol'). As a hobbyist woodturner I have lots of wood flour and shellac available so I did try it, if only for authenticity, but wasn't much impressed with the results. At the time, my main requirement was in converting EBL1 side-contact valves to EBL31 octal valves, which entailed changing the base and also changing the top cap from 3/8" to 1/4".

I ended up using 'PLASTIC PADDING SUPER STEEL EPOXY-WELD' which has proved entirely satisfactory. It has heat resistant properties well beyond what we're looking for.

This is from the maker's spec sheet:

SUPER STEEL is a dark-grey coloured, metal-filled, two-component adhesive which sets like steel and is suitable for metal, wood, china, stone, glass and leather. It hardens in 5 mins and cures in 10 mins. Max. temp 315C (<100 continuous). Contains 54g/l solvent. Suitable for metal, wood, china, stone, glass and leather Not for soft plastic and Polypropylene.

In addition to securing valve bases and top caps, I use it for all sorts of radio related tasks - Bakelite cabinet repairs, sealing the ends of 're-stuffed' capacitors and filling unwanted holes is die-cast aluminium project boxes. Despite the claim that it's 'metal filled', and its title 'Super Steel', it isn't conductive.

Some pics below:

Pic 1: EBL1 valve converted to EBL31 (new Octal base and 1/4" top cap secured with Super Steel).
Pic 2: A strip of Super Steel applied to glass, subjected to 1,000V insulation test. ('1' on the display = no conduction).
Pic 3: End view of a re-stuffed 1935 vintage cap.
Pic 4, several re-stuff caps.

It sets rock hard, can be drilled, sanded and filed.

Hope that's of interest.
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Old 12th Jul 2018, 11:32 am   #7
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Default Re: Valve base detached from glass part.

I've always been wary of using glue that sets hard when fixing valve bases due to heat expansion/different expansion rates etc possibly cracking the glass (mainly on 'hot' valves like rectifiers and output valves) so I've always favoured Evo-Stik and similar types since these never set really hard. I've never had a problem with this and if the clear type Evo-Stik is applied carefully and any residue wiped before it sets, a neat job can be achieved.
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Old 12th Jul 2018, 7:23 pm   #8
G1RAO keith
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Default Re: Valve base detached from glass part.

Thanks for all the replies everyone. The valve in question is a full wave rectifier so it will run hot but not I expect scorching hot so I may try the Evo-Stick version first, did not the original glue set hard anyway? May be the expansion and contraction of the glass caused the material to crack over time? Having said that there are plenty of valves with rock solid bases!!

Regards, Keith.
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Old 12th Jul 2018, 7:40 pm   #9
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Default Re: Valve base detached from glass part.

For rectifiers and power output valves I would recommend non acid cure silicone rubber, which comes in black or clear because it won't degrade with heating and allows for expansion and also has excellent electrical insulation properties if it is over-applied and gets down into the base/wire area.
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Old 13th Jul 2018, 12:09 am   #10
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Default Re: Valve base detached from glass part.

The original glue did set hard- but was also quite brittle and crumbly anyway, so was likely to detach before the glass came to harm. I agree with the points made about using a glue with a degree of give in it- like Sideband, I've used Evostik successfully on relatively tepid-running signal valve bases. The trouble with a modern, hard-setting glue is that it will likely be less brittle than the original shellac goop, jeopardising the glass, and matching of expansion is a grey area.
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Old 13th Jul 2018, 7:04 am   #11
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Default Re: Valve base detached from glass part.

I use Araldite or any similar 2-component glue on all types of valves, and never had a problem with a valve cracking or coming loose.

Jac
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Old 13th Jul 2018, 7:30 am   #12
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Default Re: Valve base detached from glass part.

I would back you up Jac.

I mix up a small quantity and force it between the glass and base. I then rub my finger around the join finishing off with a damp cloth.
I have done this with many valves and CRT bases without the slightest problem.
In no circumstances use 'Super Glue'. John
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Old 13th Jul 2018, 7:54 am   #13
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Default Re: Valve base detached from glass part.

Some of the cheap epoxy glues remain somewhat flexible when cured, so should allow for expansion. No doubt flexible grades of Araldite are also available at a price!
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Old 13th Jul 2018, 9:19 am   #14
David G4EBT
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Default Re: Valve base detached from glass part.

One of the key considerations mentioned at the outset and in other posts is the ability of the adhesive to withstand 'high temperatures', notably in rectifiers and output valves. However, 'high temperatures' is a highly subjective and undefined term, so it would make sense to check the temperatures of such valves. As far as Araldite is concerned, standard Araldite has a maximum operating temperature of 65C, and 'Rapid' is 80C. Thus if the valve temperature doesn't exceed that, maybe it would be fine. It's worth noting that Araldite isn't recommended for re-fixing rear view mirrors to windscreens in cars. (Glass adhesive requires UV to cure).

The original shellac/wood flour adhesive set rock hard which seems not to have been a problem in terms of risks of cracking the glass, so as I see it, any modern adhesive which sets hard and can withstand the operating temperature ought not to pose a risk . Over time, in many instances the original adhesive has been shown to have poor adhesion to glass, but in fairness, it's taken decades for the bond to break and many - perhaps most - bases (and top caps) are still firmly fixed. I my experience, it takes an overnight soaking in meths to dissolve the shellac if it's desired to remove say a cracked base to fit a new one.

Just a note of caution for anyone wishing to remove a base to replace it:

Don't just unsolder the pins and pull the base off because the wires will almost certainly spring out of place and apart from the heaters, you wont know which wire is which. They emerge from the base of the glassware in as flat 'pinch' - not in a circle. Before unsoldering the pins, I always use a Dremel with a diamond disc to carefully cut a ring about 1cm wide around the base then remove the ring so that the wires can be seen. Then I label each wire with the pin number, de-solder the pins and remove the the base. I slip a short length of coloured sleeving over each wire, using the resistor colour code to denote the pin number.
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Old 13th Jul 2018, 9:47 am   #15
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Default Re: Valve base detached from glass part.

High temp silicone rubber, DIY/builders merchants etc.

Lawrence.
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Old 13th Jul 2018, 9:52 am   #16
broadgage
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Default Re: Valve base detached from glass part.

I have recently found a new product that might be useful for re-fixing valve bases.
Called "sugru" This material is supplied in a small sealed package and initially has a similar consistency to putty, and may therefore be moulded by finger pressure to any shape.
It adheres well to most common materials apart from those plastics that feel "oily" such as PTFE or polythene.
On exposure to air it cures over about 24 hours to a firm but slightly flexible material, very similar to silicone rubber.
Unlike "araldite" and other epoxy compounds it never sets rock hard and therefore should not stress glass.
Unopened it has a shelf life of about a year, or longer if kept refrigerated.

Once opened it cures or sets, you have to use the whole, small, pack once opened.
It has a working temperature up to 180 degrees centigrade.

This material would seem to have a lot of potential for repairs in general, not just valve bases.

Sugru comes in various colours and may be obtained from numerous on line retailers including ebay and amazon.
I have no connection with the makers or vendors.
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Old 13th Jul 2018, 9:57 am   #17
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Default Re: Valve base detached from glass part.

Here's the old RCA basing cement recipe....

"This recipe for RCA's basing cement, yielding about 200 pounds of material, was "standard for all bases.":

Coarse marble flour 170 lb.
Orange flake shellac 19-1/2 lb.
Durite phenolic resin LR275-2 7-1/2 lb.
Medium-color (grade G) rosin 3-1/4 lb.
Denatured alcohol 9 liters
Malachite Green aniline dye 10 g.

(Just for reference: the above recipe yielded enough cement to put bases on 23,000 Type 50 tubes"

Lawrence.
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Old 13th Jul 2018, 10:32 am   #18
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Default Re: Valve base detached from glass part.

High temperature silicone as used for the glass in oven doors is generally black and generally acceptable for valve bases. There's a very high temperature version used for sealing flues, but it's orange and may not look good on a valve base.
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Old 13th Jul 2018, 1:14 pm   #19
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Default Re: Valve base detached from glass part.

The very high temp silicone flue sealant is also available in black, ebay.
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Old 13th Jul 2018, 3:12 pm   #20
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Default Re: Valve base detached from glass part.

I agree with David G4EBT, Plastic Padding works well I have used it on KT66s.

I recently bought some Devcon 2 Ton epoxy I have not tried it on have bases but seems good, Up to 93c, so might work.

Trevor
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