Heat-resistant epoxy and similar materials (for a tube adapter)?

[rock soderstrom]

Hi guys, really good German steel tubes are slowly becoming unaffordable. That's why I've been experimenting with DIY tube adapters for some time now, which works pretty well.



My question is, which material is suitable for electrically insulating my adapters? A little more mechanical stability would be another goal, although the basic construction is already surprisingly stable.

What would you use to mould the base adapter? Epoxy? Or is there perhaps even a material for the hot glue gun that can do the job?

 

[rock soderstrom]

To clarify, I'm talking about a 1-2mA preamp tubes, nothing that gets really hot...

 

[JohnRoberts]

Hot melt may melt too easily. Of course you can try it and see how it behaves.

The good thing about hot melt is you can go back in if you need to make repairs later.

JR

 

[Rusan]

About 20 years ago, I made some adapters for a guy so he could substitute 6CG7/6FQ7 for 6SN7. I filled the void space between the octal tube bases and noval sockets with red RTV silicone hi-temp gasket sealer, for temperature resistance and vibration damping. AFAIK, they're still in service; haven't conversed with him in several years.

 

[rock soderstrom]

Hot melt may melt too easily.

Yes, I expect that too, although there are a surprising number of different materials for the hot glue gun. Perhaps one that has a higher melting temperature after melting once? I will try out a few in the coming days...

The good thing about hot melt is you can go back in if you need to make repairs later.

+1

I filled the void space between the octal tube bases and noval sockets with red RTV silicone hi-temp gasket sealer, for temperature resistance and vibration damping. AFAIK, they're still in service; haven't conversed with him in several years.

Interesting, I do not know this stuff, I will take a closer look. Does this material become hard or does it remain soft like silicone?

 

[chrispbass]

Yes, I expect that too, although there are a surprising number of different materials for the hot glue gun. Perhaps one that has a higher melting temperature after melting once? I will try out a few in the coming days...

+1

Interesting, I do not know this stuff, I will take a closer look. Does this material become hard or does it remain soft like silicone?

There are high temp silicones as well that will prob suffice in this scenario.
Sounds like you have good mechanical strength, so it’s more of a way of tidying it up and a “wet paint do not touch” scenario (with regards to safety), but it’s diy and not a commercial product.

On a side note, when I was about 14, my friends sisters bf asked me if I would replace the head gasket on his motor bike. Can’t remember the make now, but I agreed, and I went to his house to start the job, and he’d bought a couple of tubes of RTV (room temp vulcanising) gasket sealer thinking it would be good enough. It was one of those moments when 1. He was asking a young teen to strip down his prized motorbike, and 2. He hadn’t considered that he needed a proper gasket kit!

I persuaded him that he really needed the gasket kit, stripped it down, re-timed the cams and breathed a sigh of relief when he kicked it over and it started up after rebuilding it.

 

[k brown]

Yes, I was going to suggest silicone too. For preamp tubes you probably don't even need the hi temp stuff.

For the GE products, be sure to get the glue, not the sealant. Good at up to 400 degrees:

https://gesealants.com/wp-content/uploads/2023/04/TD-GE-Silicone-2-Household-Glue-2024.06.01.pdf

https://www.amazon.com/Silicone-Hou...223019&sprefix=silicone2+glue,aps,229&sr=8-10

 

[thelivingroom]

Yes, I expect that too, although there are a surprising number of different materials for the hot glue gun. Perhaps one that has a higher melting temperature after melting once? I will try out a few in the coming days...

+1

Interesting, I do not know this stuff, I will take a closer look. Does this material become hard or does it remain soft like silicone?

The red RTV remains fairly soft. There are different colors for different applications that you can check out at an automotive store, and some become more rigid than others. Some may also have something conductive mixed in them (not the red one though), so be cautious of that. It’s been over 10 years since I last built a car engine, so I’m a bit fuzzy on which ones did what, but I do remember using a grey one that dried pretty rigid.

 

[craig]

Your standard epoxy is good to 200c

 

[Evertide]

Your standard epoxy is good to 200cView attachment 135967

Temperature resistance -30°C to 65°C

 

[rock soderstrom]

Okay, out of curiosity I used black hot glue. First of all, it works without any problems with an EF86, which only gets lukewarm at the socket.

I used wood veneer as a mould, which wasn't particularly clever, it takes half an eternity to get it all off again.



I used this hot glue, it gets rock hard, the adapter almost feels like an ice hockey puck now.



The whole thing doesn't look very nice, I tried to sand the surface, but it doesn't work and look even worse afterwards.


But the function is great, the mechanical stability is now very high, it holds bombproof.

Next time I'll use a suitable plastic tube as a mould and just leave it on, that will also look better.

For hotter preamp and driver tubes, I would use something more temperature-resistant. Thanks for the suggestions!

Edit: I needed almost two 28cm sticks of glue, diameter 11mm. That's quite a bit of material you need. One advantage of hot glue is that it is very inexpensive.

Edit2: its a EF86 for EF12k adapter

 

[Hubbub]

One way to clean up a messy hot glue job is to use a hot air rework station air tool. The amount of heat is easily controlled, and it melts those pesky stringy bits quickly.

 

[mihi_fuchs]

Okay, out of curiosity I used black hot glue. First of all, it works without any problems with an EF86, which only gets lukewarm at the socket.

I used wood veneer as a mould, which wasn't particularly clever, it takes half an eternity to get it all off again.

View attachment 135974

I used this hot glue, it gets rock hard, the adapter almost feels like an ice hockey puck now.

View attachment 135975

The whole thing doesn't look very nice, I tried to sand the surface, but it doesn't work and look even worse afterwards.

in 3d printing you often use acetone to clean the edges off. maybe that works here too?

View attachment 135976
But the function is great, the mechanical stability is now very high, it holds bombproof.

Next time I'll use a suitable plastic tube as a mould and just leave it on, that will also look better.

For hotter preamp and driver tubes, I would use something more temperature-resistant. Thanks for the suggestions!

Edit: I needed almost two 28cm sticks of glue, diameter 11mm. That's quite a bit of material you need. One advantage of hot glue is that it is very inexpensive.

Edit2: its a EF86 for EF12k adapter

looks really nice. have you considered actual real 3d printing? you could print half of the insulation, fit in your connector and print the second part around to hold it tight. at least the insulation of the material would be good enough i guess.

 

[capacitorless]

I've also used large diameter heat shrink tubing, to cover up my own less than visually ideal projects Easy to cut off if needed and fills in the gaps (natch) as it gets hot. Something like this 2" 3:1 shrinking stuff at Amazon could work.

 

[k brown]

Okay, out of curiosity I used black hot glue. First of all, it works without any problems with an EF86, which only gets lukewarm at the socket.

I used wood veneer as a mould, which wasn't particularly clever, it takes half an eternity to get it all off again.

View attachment 135974

I used this hot glue, it gets rock hard, the adapter almost feels like an ice hockey puck now.

View attachment 135975

The whole thing doesn't look very nice, I tried to sand the surface, but it doesn't work and look even worse afterwards.

View attachment 135976
But the function is great, the mechanical stability is now very high, it holds bombproof.

Next time I'll use a suitable plastic tube as a mould and just leave it on, that will also look better.

For hotter preamp and driver tubes, I would use something more temperature-resistant. Thanks for the suggestions!

Edit: I needed almost two 28cm sticks of glue, diameter 11mm. That's quite a bit of material you need. One advantage of hot glue is that it is very inexpensive.

Edit2: its a EF86 for EF12k adapter

Do those black sticks require an unusually hot gun?; I've never seen them.

 

[rock soderstrom]

Do those black sticks require an unusually hot gun?; I've never seen them.

No, they work perfectly with any hot gun.

I've also used large diameter heat shrink tubing, to cover up my own less than visually ideal projects Easy to cut off if needed and fills in the gaps (natch) as it gets hot. Something like this 2" 3:1 shrinking stuff at Amazon could work.

Good idea!

One way to clean up a messy hot glue job is to use a hot air rework station air tool. The amount of heat is easily controlled, and it melts those pesky stringy bits quickly.

+1
ordinary glass cleaner also works surprisingly well to remove hot glue, especially on flat surfaces

in 3d printing you often use acetone to clean the edges off. maybe that works here too?

I will try that!

have you considered actual real 3d printing? you could print half of the insulation, fit in your connector and print the second part around to hold it tight. at least the insulation of the material would be good enough i guess.

Unfortunately I don't have a 3D printing possibility, I think here you are better positioned with a liquid mass, because it also runs very well into the gaps and stabilizes the whole thing enormously!

I'm going to try that out too. I'm curious to see how hard it gets when it's dry.

 

[Paul W]

Temperature resistance -30°C to 65°C

I'd use a high-temperature epoxy if you're going to use epoxy.

Normal epoxies are often less heat resistant than they sound from simple numbers on the package. Well below their rated maximum temperature they'll soften and creep and weaken.

(I learned that making molds for vacuum forming. Going by the maximum temperature on the package, you'd thing that epoxy resin would be better than styrene resin, but it's worse. Styrene holds up better to repeated high temperatures and physical stress.)

 

[capacitorless]

I'm not at all sure that this is germane for this particular application, but some epoxies shrink a little (the 'web quotes around 3.5% on average) during curing. There are special formulations that don't in the practical sense, but I'm guessing the typical stuff does.

 

[k brown]

In the realm of epoxy, I was thinking more interms of epoxy putty, rather than 'liquid'.

I think it shrinks less, and can be shaped and smoothed with damp fingers. just don't get the stuff with metal powder in it!

i imagine the version for wood, would have no conductive ingredients.

https://www.amazon.com/J-B-Weld-8258-KwikWood-Repair/dp/B005493KM2/ref=sr_1_5?crid=EZ8F1A7N7BOZ&dib=eyJ2IjoiMSJ9.rXEYkfa7ZRKYtQUjaBcJxmxzpMdDkhc8LIB1JqJyax27JBMKEQljOfTi-yw0ZbHfNokpQiYEV-ziK18eSQ8vY4yM_1mcgPg_KFd-0b39621qLai19aOb7b0sXOc1cfspBxiWYCJKBKgnSkbNgms6CV-ZDsPV5UNablurb_5nLh1cLH39M8A876-p9J-SI-OxpVNCCFhuvHy3drJ8sz2M23qv20RzXz8KGIqzHKTvBNkgJdVCqmVo13-I1q6rWz5AXx3SuWtNnDYf3L5fR2A4ku4ZWUGUNUGdCJxb58cmTEk.oQ85YEaOZ-7-s3WmUapVFF8r7UTc5pGe1grjcisCaOE&dib_tag=se&keywords=epoxy+putty+for+wood&qid=1725300332&sprefix=epoxy+putty,aps,182&sr=8-5

 

[capacitorless]

Haha, no original JB Weld! Awesome stuff btw.

(edit: to be clear, I'm not suggesting this for the tube adapter being discussed, rather the opposite)