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White rubbery power tranny insulators

Not mica and not the grey plastic-like stuff, anyone familiar.? They are on a Kustom 6160A mixer amp, USA Kustom , not Custom, under TOP66 trannies. They have shrunk on the upper section (hottest ?) to the point of very nearly shrinking under the tranny bodies and the uncovered parts are ruffled, showing the heated area has shrunk significantly, even split possibly, not taken apart yet, although check out cold ok. No other over-temperature indications. I will replace with mica but is this usual for these, I've not come across white , relatively thick rubbery ones before. Almost look like thin slabs of slicone bath sealant.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook
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They are probably silicone rubber with some fiberglass imbedded to make them puncture resistant.

Silicone takes high temperatures very well, never saw one that deteriorated with heat - yet.

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Reply to
default

Like this?

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I have never had trouble with them shrinking.

Chris

Reply to
Chris Jones

You can get the synthetic insulators in many colours including white, (rust) red and green.

The white (and green) ones tend to be high performance (low thermal resistance) so you may be degrading performance with a typical mica washer.

Graham

Reply to
Eeyore

Likewise.

The 'ruffling' merely means the washer has been subjected to some serious mounting pressure. The nice thing abot these flexible washers is the 'conform' i.e. mould themselves to surfaces underpressure which enhances the heat transfer.

Graham

Reply to
Eeyore

TOP66

across

Probably the same

This picture shows one

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the part at "A" has almost shrunk under the tranny. None of the material looks heat damaged as its all the same tone of white.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook

It's NOT shrinkage ! The pad has simply conformed to the surface.

Graham

Reply to
Eeyore

white.

The trannies are flat-backed as is the heatsink, no convexity/concavity. Assuming the pads were rectangular to start with, the tops of each of the 4 trannies are now 6 to 8mm narrower than the bottoms. The ruffling is on the outer edge, the original dimension. If the material had been squashed then the ruffling would be on the inner exposed edges. Will probably take apart today after on-load powered-up testing

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook

I'm getting a bit confused on the thermal characteristics. Thermal conductivity of this silicone material in W/(m*K) at 3.5 is about 10 times better than mica at 0.35, silicone grease about 0.2 . At least I know its the minimum amount of grease to be used, it annoys me coming across amps with great dollops of the stuff all around that gets on your clothing.

But the thickness at 0.4 mm is about 6 times thicker than the 0.07mm mica washers I would use. What is the final relative de-merit of using mica instead of white silicone pads ?

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

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Reply to
N Cook

followup: see thread

"Mica versus Silicone pad insulators"

Reply to
N Cook

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