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Old 23rd August 2003, 10:19 AM   #1
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Default Odd Heatsink Compound

Working on an old Pioneer SX-1010, and having problems with the bias current stability. If I set bias, and operate with no load, I can walk away for hours and come back and it is still reasonably close to where I set it.

However, if I attach a dummy load and heat the amp up a bit, bias rises (from 50mA to 75 or so) and it takes forever for the amp to cool down after the load is removed. I mean, hours....then and only then does the bias drop to fairly close to my setting.

I examined the drivers and outputs, and it appears that Pioneer used some sort of wierd clear heatsink compound on the mica washers. Almost like clear fingernail polish...I've never seen it before (but then again, I haven't worked on that many Pioneer's).

It doesn't come off easily, but I did the best I could and applied the standard white compound. Haven't had a chance to see if it makes a difference in cooling or bias stability as I am still missing a few parts to finish the job.

Anybody else see this stuff? Shouldn't the regular white stuff be better? (It's certainly not cleaner, though)
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Old 24th August 2003, 08:50 PM   #2
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i've come across stuff matching yuor description in an old Jansen 100W powered mixer. can't tell you anything about how good it is as the mixer died shortly after i bought it. when i rebuilt it tho i used standard issue zinc oxide based thermal paste (white stuff) and it keeps it nice and cool

alternately, i bought a tube of silver based (10% silver) thermal grease for my new computer processor and had heap of it left after installation (you only need a pathetically small amount, and it only comes in 1g or larger tubes!). so since then i've been using it on my amps and it does brilliantly. its thermal resistance is listed as 0.06C/W which is MUCH better then Zinc oxide

so to answer your question, wouldn't have a clue

cheers
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Old 24th August 2003, 09:41 PM   #3
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For amplifiers with eight or more output devices, the silver gets used pretty quickly. If the zinc oxide is good enough for 99% of manufacturers, and of course it is cheap, then I'll stick with it.

...was just wondering if anyone else had seen this stuff (the clear junk). Must not have been very common, and must not have worked that well or else everybody would be using it...
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