Heatsink silicone pad or compound
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The difference is 'Silicon pads', are a one-time use item, and have very slightly better heat conduction properties. Whereas 'Silicone compond' (the white stuff ONLY) uses Mica washers (as insulators) which if they are treated VERY carefully can be used many times. With either you need to be very careful that you don't trap metallic waste in the pads, or in the white stuff - absolute cleanliness in this regard is required for either to be a success.
Personally I always use the white stuff (never ever the 'silver' stuff) and Mica washers - because that is what is fitted to all my vintage gear - but I wouldn't hesitate to use 'pads' if that was what was used originally.
Personally I always use the white stuff (never ever the 'silver' stuff) and Mica washers - because that is what is fitted to all my vintage gear - but I wouldn't hesitate to use 'pads' if that was what was used originally.
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restorer-john
Addicted Member
Silicone heat transfer compound is preferred in most cases. Yes, it's a bit messy, but it lasts forever, and, correctly applied, offers a much more intimate fit to the heatsink/mica.
I never use sil pads unless the gear uses fans- as fans pull a lot of dust through gear that 'sticks' to silicone paste.
I never use sil pads unless the gear uses fans- as fans pull a lot of dust through gear that 'sticks' to silicone paste.
I've had problems with oscillations using "Sil-Pads" on some vintage amplifiers, Phase Linear 400 and an old Quatre. I know in the Phase Linear service manual it says to get rid of the Sil-Pads if you experience oscillations. Mica and compound never cause a problem except it can be messy.
ConradH
Lunatic Member
There are many different grades of silicone pad. The old cheap grey ones aren't that great. The expensive pink ones can be very good. For me, it depends on power. In a low powered receiver I'll use the high quality Sil-Pads without a second thought. For a higher power amp my favorite thing is grease and hard anodize insulators. It's hard to do better. Crown uses/used them. Lacking those, I'll use mica, but it has to be thin mica. Mica is not a great thermal conductor. It only works well if it's very thin.
savatage1973
Addicted Member
Mica and compound--the only way to go...
Ditto------
tyeeslayer
Super Member
The mica insulates the transistor from shorting against the metal heatsink. Yes thermal compound goes on both sides of the mica.
whoaru99
Epic Member
With the heat sink compound a little goes a long way. If there is a bunch squishing out probably too much was applied. The compound is not there to form another layer, per se, but only to fill the minute voids due to minor surface imperfections that would otherwise be filled with air.
Also, where there is mica (or other insulator) there is often insulated bushings for the transistor mounting hardware. Be sure that goes back exactly as it was. And, lastly, smoking down the screws isn't necessarily best. There is an ideal torque range and it's not usually as tight as they could go.
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savatage1973
Addicted Member
YUP--want a short, crank it down until it nearly strips!!!
savatage1973
Addicted Member
"Snug" and no more--so you are about right. If you have to put "effort" into it, you have gone too far. You can actually damage the transistors (metal can types) due to warpage if you crank them down.
