On Fri, 27 Aug 2010 08:29:01 +0100, "N_Cook"
wrote:

Any opinions on silipads? From my limited trials mica sheet and absolute
minimal white grease has better thermal transfer. Emphasis again on minimal.

Do the math. Silicon impregnated rubber TO-3 pads have a thermal
resistance of about 0.4K/watt. 0.0002" Mica, with silicon grease
smeared on both sides is about 0.6K/watt. Depending on your total
power dissipation, that's hardly any difference. However, if your
heat sink is undersized, buried inside a cabinet, or located in a
place where there's no air flow, it might make a difference.

http://www.wakefield.com/LinkClick.aspx?fileticket=1ULQQwz8xmU%3d&tabid=64
See Page 6-8. The example shown is for a TO-3 packaged device.

Having to decide this week whether to spend out on 6 MJ series TO3 devices
in an old Carver amp failed due to one of the driver TO3 being pushed
through a heap of white grease , so grease on pins getting inside the TO3
socket housing , so insulating partially and eventually burning up the pin .

Keep it stock. However, if this is a push-pull type of amp, where the
thermal balance of the xsistors has an effect on the bias point,
crossover distortion, and possibly linearity, I would make sure that
whatever you do to one side, the same gets done to the other.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558