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#10
August 14th 04, 05:28 PM
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On Fri, 13 Aug 2004 12:54:14 +0000, Mike Andrews wrote:
In (rec.radio.amateur.homebrew), Fred Bloggs wrote: Paul Burridge wrote: On Fri, 13 Aug 2004 03:49:15 +0000 (UTC), (Ken Smith) wrote: Theres no problem getting 10mA to flow in a FET with Idss of 5mA. Just apply a positive bias to the gate. I've had as much as 2 or 3 A flow through a JFET this way. How many mS did the Fet last? I suppose you could always stand there with a can of arctic spray directed on it, but I doubt the customer would be impressed. ;-) Actually there have been systems produced that did run quite hot and were arranged with a liquid nitrogen drip onto the electronics to keep things cool. One model of Seymour Cray's computers ran with the logic immersed in a bath of chilled Fluorinert or some such, with a fairly hefty pump to keep the coolant recirculating through the chiller. Many years before, IBM was going to use a CFC (FC86, IIRC) in much the same way. The logic modules were about 4" cubes with a multi-layer (50-60, can't remember) ceramic substrate with 100 logic chips on one side, a water-filled cold-plate on the other, and filled with the CFC. Heat was removed from back-side of the chips by boiling the CFC. I worked on a logic tester in '75 that immersed the un-encapsulated substrate into a bath of CFCs so it could be probed. Unfortunately, boiling the CFC also distilled it, leaving any contamination on the chips. The result came to be known as the "black plague". Because of the "black plague" the "LEM" (Liquid Encapsulated Module) was replaced by a similar looking (though shorter) "TCM" (Thermal Conduction Module) which used pistons on the backside of the chips (increased to 121 chips) to transfer heat (10W per chip, 1200W total) to the cold-plate and filled with helium. The TCMs were used throught the '80s and early '90s for the high-end ECL systems. -- Keith |
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