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Potting compund question
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innkeeper:
I am looking for what to use for potting compound.

I've built myself some solid state rectifier replacements for tube rectifiers into tube bases, mostly for testing purposes.  Which means i will tend to be plugging them in and unplugging them a lot (not live of course).

I want to pot them so i don't mess them up.  When I looked at some potting compound from GC it was like 50 bucks.  I' looking for a suitable CHEAP potting compound that is solid somewhat thermally conductive, and won't break down over time and become conductive.  voltages involved will be under 500v .. actually for my initial uses probably under 200v
floobydust:
I've put silicon diode strings into 866 rectifier 4-pin sockets, you don't have to pot them.
Just need a lid to keep it safe.
I've blown up 3kV solid-state diode strings and you would not be able to fix that once it is potted... so your design has to be good, not just a bunch of diodes in series.

But if you want to pot them, I would use silicone encapsulants which cure like a hard rubber.
The two-part ones perform better but more expensive and messy to mix, like Dow Corning SYLGARD 170. You might try for free samples. Potting compound can leak out the tube socket pins which makes a mess.

RTV silicone with a dielectric rating would be okay. GE RTV6700 is at the hardware store and 16kV/mm. I don't like GE's latest environmetally friendly products, I've had some that never cure.

Heat is not so much an issue because little is generated in solid-state diodes, at typical plate currents. Unless you are putting in series resistors to try match the tube's internal resistance. Most potting compounds help transfer heat.

https://www.mgchemicals.com/products/rtv-silicones/potting-compounds] [url]https://www.mgchemicals.com/products/rtv-silicones/potting-compounds[/url]
coppercone2:
Hmm what you might wanna do with a cheap compound is embed some thermocouples into your PSU (use thermal epoxy to attach them to the relevant places before potting) and measure them once they are running. I am planning on doing this, so I can scan  the assembly later, if I ever get around to potting anything. If you make them yourself from wire and give them a quick test it should be very cheap, then you can leave them as test points you can hook into for trouble shooting or integrity test to see if something is deciding to get hot like 6 months or 6 years later. It's also generally interesting.

Keep in mind too you can route some wires out of a potted prototyped you soldered to relevant places to act as test points, so you won't be completely in the dark if something is wrong and you can get an idea of what to do maybe on v2 without difficult de-potting.
innkeeper:
floobydust, just capping it might be the option i have to take. seems the potting options are outrageously priced.
coppercone2:
Can you cut a tube with a glass cutter, do a even cleave and then glue it back together? I wonder if that glass can take it. Possibly put a thread in it so it can be opened up. Using a piece of threaded pipe would probobly be safer though since its not a glue seal. It seems like you can use a bit of copper pipe thats soldered shut. But their conductive, I don't know if you can trust a big heat shrink insulator in a high temperature area surrounded by vacuum devices.

I am not sure what a good solution would be to enclosure. What are you using? I imagined a copper pipe that has a bunch of threaded feedthroughs soldered to it, with the stuff inside, and then the feedthroughs soldered to the tube socket by heavy gauge stiff wire and some kind of reinforcement glue, then ground the whole thing to be safe. Using star washers etc.
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