Mica versus Silicone pad insulators

N Cook · 2007-09-11T15:29:38+00:00

I was not convinced that for an existing used amp with 4x TOP66 power outputdevices that the silicone pads were better than mica.Each of the 4 insulating pads had shrunk about 5mm at the tops (hottest)compared to bottoms , ruffling the original outer edges, heat damage ?.I replaced all 4 with mica and thin films of thermal grease.Before doing so I powered up the amp with 400 Hz cointinuous sine giving 20watts in a dummy load. No fan cooling for this amp, justconvection/radiation.Laid a brass barrel protected thermometer on the heatsink and tookmeasurements. Stabilised at 33 deg C over ambient after 50 minutes.Replaced with mica and redid the load test.For same ambient , same testing position/attitude, power in load etc it nowtook 30 minutes to stabilise at plus 32 deg C over ambient.More graphically , but less scientific, - the finger test.After half an hour of heating with the mica setup I could hold a fingertipon each tranny for about 5 seconds before finding it uncomfortable.Previously half a second of fingertip touch was enough.Any comments ?--Diverse Devices, Southampton, Englandelectronic hints and repair briefs , schematics/manuals list on

Sep 11, 2007 45 Replies

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Eeyore 18 years ago

Warth's K52 material is specified with a mounting pressure of as low as 10 psi. It's barely much higher at 10 psi than it is at 200 psi.

Graham

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Meat Plow 18 years ago

I used to use them all the time with low power amps. They were (back when I used them) not strong enough to provide adequate torque for high power applications although I have seen them in use for things like audio output bricks in car stereos.

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Meat Plow 18 years ago

Amen to that.

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Meat Plow 18 years ago

Take your meds and a long nap.

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Eeyore 18 years ago

Nylon is totally unsuitable in such an application.

Nylon naturally has some water content which will be driven off in high temperature use and this causes shrinkage with unpredictable effects. It also seems to embrittle it. I also wouldn't trust a nylon screw to reliably provide the required mounting torque either.

Graham

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Michael A. Terrell 18 years ago

At the bottom of a lake.

Service to my country? Been there, Done that, and I've got my DD214 to prove it. Member of DAV #85. Michael A. Terrell Central Florida

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