Potting Trannys

[Blair]

Has anyone here ever potted a toroid? I have my stereo 60wpc amp with an ANTEK tranny. The only real complaint I have is that it has a wicked low pitched hum not audible in the signal, but actually from the tranny. I'm just curious if anyone has ever taken silicone caulk and potted their tranny. Heck at $45.00, it may be worth the experiement.

Ideas, suggestions?

Blair

[mesherm]

I wouldn't use any silicone that has a acetic acid odor (vinegar). All of those silicones need as much air exposure as possible to cure and won't cure up properly in thickness over about 3/8 inch thick. The outside will cure but the inside will remain gooey. You need to get the silicone made for potting. The old trannies used a type of tar. These days, epoxy is usually used that is made for potting and has a heat conducting filler added.
The best way would be to vacuum pot the tranny in some sort of metal case. By that I mean adding the mixed epoxy and then pulling a partial vacuum on the whole casting so that the air is removed and as the vaccum is released the epoxy flows into all the inside nooks and crannies. You would be suprised to see how much air is trapped in the epoxy just from mixing. You would have to place heavy paper around the metal can because as the vacuum is pulled the epoxy froths up almost 3 times the initial volume depending on the viscosity.

http://www.solarcompounds.com/products/epec.asp

[Blair]

I see. So, it won't really cause heat issues being potted. I had planned on using high heat automotive silicone for this in layers. I can't find the price sheet on that stuff you provided the link for.I guess another option would be to use rubber bicycle intertube wrapped around the tranny inside the metal pot I want to use to absorb the noise. I'm just wanting to shut this thing up. It is annoying during soft passages.

Thanks for the link. What do you think about the innertube?

Blair

[mesherm]

Innertube rubber is probably good to at least 250 F. No harm in trying it to see how hot it gets. Is the chassis made of steel? If the hold down bolt through the center of the toroid makes a complete one-turn connection it acts just like a low voltage high current winding. Do you have a rubber pad on both sides of the toroid?

[Blair]

Yeah, I have the rubber pads on top and bottom, and there is a steel plate it mounts to, but most of the chassis is actually wood. I don't think it will get too terribly hot. I'll see. It is a very nice tranny. Especially for the price. I just wish it were a bit quieter. None of this can really hurt. Another option would be to pour a few high heat silicone gaskets that are a bit thicker to replace the rubber pads with. They aill be more absorbent, and likely damp the sound better.

Thanks for the ideas,

Blair

[mesherm]

The innertube idea may work ok then. Just wrap a couple layers around the toroid and re-fasten it. Maybe instead of the rubber pad, just put three thick rubber pieces between the tranny and chassis 120 degrees apart like a tripod. Reduce the physical contact to a bare minimum.
I have used a lot of those toroids and have never found one to be noisy. Usually its an old EI tranny I get off of ebay that hums.

[Blair]

I'll try it. It is probably not really that noisy. I know it is there, and I'm young. I can't sit in a room with a computer processor whining for more than an hour without going nuts. Not that I'm not a bit off anyway Yellow_Light_Colorz_PDT_09

I'll see what I get.

Thanks,

Blair

[dhuebert]

Here is something I said about silicone cement a few years ago which may bear repeating:

When I first started building electronics for medical research, I used RTV to protect some of my electrical connections. I experienced several failures which could sometimes be quite expensive as a whole days experiment would be trashed. I spoke to an engineer at Dow-Corning and he explained that RTV had ascetic acid as its volatile component, and, after the RTV was finished curing, it was left at a slightly low ph (acidic). This produced a galvanic reaction between the copper and solder causing the joint to fail. I was supplied with a sample of sealant that had no volatile component; end of failures. As a side benefit, since there was no volatile, it did not shrink during cure. I would not recommend RTV for electronics work.

Don

[Blair]

I appreciate that. It will definitely assist me in my experimenting. Plus save me a few bucks in Trannys. It is not that loud at all, but I can hear it. One of those things where everyone in the room doesen't comment on it, but I definitely know it is there.

I think since this pan I'm going to use is a bit larger than the toroid, I'm going to try to damp it first and securely adhere it to the chassis. I can't hurt the pan, and it is cheap to replace.

Thanks,

Blair