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Thread: White Thermal Grease Vs Clear Crown CE 1000 Amp

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    White Thermal Grease Vs Clear Crown CE 1000 Amp

    Hello all, Im currently involved with the repair of a Crown CE 1000 Solid State . Most say these amps are B.E.R. , and Iím beginning to understand why. Hundreds of SMDís and fragile double sided pcb that cannot be fully tested without complete removal from its solid bottom chassis, and using custom made jumper wires, or their service kit. Question: main power output transistors call for white thermal grease (per Crown service manual). I understand this as the common white silicon based thermal compound Iíve been using for years on transistors and even cpuís. The driver transistors TO3 type per Crown are requiring CLEAR Thermal Grease between them and the aluminum power output heatsink. I have never seen or used CLEAR Thermal grease. Why would Crown be calling for the usage of two different types?
    Iím aware some such as the white being non electrical conducive, and metal based type greases that can be conducive. But what is clear thermal grease? The drivers Qís do have their collectors attached internally to the outer metal backing plate of each transistor, which then bolts directly to the aluminum heatsinks. Yes there is one insulated channel and one uninsulated, one channels heatsink does appear powder coated black, the other heatsink bare aluminum, but the clear Thermal Grease is specifically called out for usage on both heatsinks for only the drivers. Anyone know what or why clear Thermal would or should be used? Does anyone know where it could be purchased from other than Crown, if really necessary ?

    Thank you

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    Are those the only transistors that don't use the mica insulators? If so, I wonder if it has something to do with that. Seems to me the clear stuff is a bit thinner and less prone to drying out.
    Not sure why they wouldn't just use it for everything though. Maybe it's more expensive.

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    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

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    Quote Originally Posted by g1 View Post
    Are those the only transistors that don't use the mica insulators? If so, I wonder if it has something to do with that. Seems to me the clear stuff is a bit thinner and less prone to drying out.
    Not sure why they wouldn't just use it for everything though. Maybe it's more expensive.
    Each channel uses eight MJ21194 TO-3 Metal Can style per channel (4 on each of 2 heatsinks per channel, 4 heatsinks total for both channels) , only one output transistors per channel of 8 is using a Mica insulator and bolt eyelet insulator sleeves. The Drivers that Crown calls for using the clear thermal grease to the output heatsinks do not use mica insulators at all. These drivers are 2SC5242 TO-3P style with collector attached internally to the metal back of the transistor. Just donít understand the reasoning for calling out Clear Thermal Grease for just the drivers? See attachment with notes, this heatsink shown is 1/2 of one channel, and is the only heatsink on this one channel that uses insulated mica hardware for one of the output transistors. You can see the driver mounted on the side of heatsink.
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