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bakelight block potting compound????? - Printable Version

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+--- Thread: bakelight block potting compound????? (/showthread.php?tid=18325)


bakelight block potting compound????? - falcon123 - 04-29-2018

im about 1/2 way through my '34 84b. got the last cap i needed yesterday. one other website advised using dap concrete joint tar to fill the blocks, originally close but yuck! i dont plan on doing anything till the set is ready to go back in its cabinet any way.i was tempted to leave them empty, but because of the high voltages involved i was concerned that dust and such may be a problem, i briefly considered candle wax and 3140 rtv.what do you fella's advise???

RE: bakelight block potting compound????? - Radioroslyn - 04-29-2018

Repotting is unnecessary just solder in the new cap (s) and remount to chassis.

RE: bakelight block potting compound????? - Ron Ramirez - 04-29-2018

What Terry said.

DO NOT use silicones. Do not use concrete joint tar. Just do as Terry advised. Icon_thumbup

RE: bakelight block potting compound????? - morzh - 04-29-2018

Second ditto.
Potting is a waste. It was necessary as they used shell-less capacitors that needed some sort of insulation from the environment. You are putting new caps in it that are already self-sufficient. No potting required.

RE: bakelight block potting compound????? - Ron Ramirez - 04-29-2018

To me, it makes sense to pot the older Philco tone control switches since the area where the capacitors are placed is exposed. In this case, I do not recommend using anything other than hot glue.

For bakelite blocks, there is no need to re-pot those.

Silicone is nasty stuff. It will eat copper. A fellow I know who is on the other forum and AK once told me a horror story about a box having been potted with silicone, and after the circuit in question stopped working, he inspected the box to find that all of the wiring had disintegrated from the silicone.

Hot glue is a good insulator and will not harm modern yellow film capacitors. The hot glue will hold those new tone control caps in place in the old Philco tone control switches and gives a more professional appearance. But to use it in regular bakelite blocks is superfluous.

One more thing. Don't use hot glue on modern electrolytics. Don't ask how I know. Icon_eek

RE: bakelight block potting compound????? - morzh - 04-29-2018

I always pot tone control with hot glue but then it is very different and the plastic will act as stabilizer plus insulator for 2-3 caps that are really crammed there.

RE: bakelight block potting compound????? - falcon123 - 04-30-2018

i was leaning that way anyway and thanks, empty they shall stay. by the way though 3140 is an electronic grade silicone that DOES NOT contain acetic acid. its runny and can be painted with an acid brush and as i recall was the ONLY rtv cited in the old navy aircraft wiring manual. i know very well what all the other stuff does! you should see what it does to canon plugs when used in lieu of a packing grommet!

RE: bakelight block potting compound????? - Arran - 04-30-2018

I believe that falcon is right, it's the acetic acid used in things like bathtub caulking that's the issue, it has a noticeable vinegar smell, however I found out that Permatex windshield and glass adhesive does not have acetic acid so it's safe, there may be others that are as well. But getting back to the Bakelite blocks, it isn't necessary to repot those, the new caps are already weather tight. I don't know how much dust would get into them considering that they are under a chassis, which either has a bottom plate or is screwed down to a board, the underside of a chassis is usually the cleanest part of the radio unless a rodent got in there somehow.
Regards
Arran