Does Anybody Else Do This?
- Thread starter mlucitt
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The purpose of the grease is to fill in tiny air pockets between the two surfaces. Less is more. When used sparingly the grease won't hurt anything. I doubt you would see a significant difference. Since there are several boards being built it would be possible to do some testing. Build a couple boards with grease and a couple without and check temperature rise. Some multimeters have inputs for thermocouples. The alternative is to get a thermal gun off ebay/amazon. They cost at least $20.
In recent years I've been taking temps on the outputs with amps under load. I run the amp at 1/3 power which makes for max temp on the outputs. By shooting the TO3 case with a gun I can confirm the screws are adequately tightened and the transistors are sharing the load. It probably comes as no surprise the ouptuts at the top of the heatsinks are a few degrees hotter than the bottom ones. The location of the heatsink on the chassis matters to, but it's a only a few degrees. I've had case temps over 100 degrees C. for a half hour or more and no failures. Makes you wonder how hot they are when they do fail.
In recent years I've been taking temps on the outputs with amps under load. I run the amp at 1/3 power which makes for max temp on the outputs. By shooting the TO3 case with a gun I can confirm the screws are adequately tightened and the transistors are sharing the load. It probably comes as no surprise the ouptuts at the top of the heatsinks are a few degrees hotter than the bottom ones. The location of the heatsink on the chassis matters to, but it's a only a few degrees. I've had case temps over 100 degrees C. for a half hour or more and no failures. Makes you wonder how hot they are when they do fail.
I used to use silcon grease and then the Thermal compound from Avid but now days it is easy to get Silpads from off E bay pretty cheap for TO-220 transistors. There are really high end insulators that you can obtain but a properly designed item will not demand too much from a single device unless it is designed in China where the boards will turn brown from excessive heat. There are beryllium copper or item I saw in old Transmitters. I think they were TO-3 mounts.
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Affirmative on the thermal grease here, but only on the control board.
I thought about using them on the outputs but decided against it. If I used mica insulators I probably would give ‘em a tiny schmear. Retrospect: maybe a little dab under the rectifier would have been an option to pass some heat to the filter cap saddle.
I thought about using them on the outputs but decided against it. If I used mica insulators I probably would give ‘em a tiny schmear. Retrospect: maybe a little dab under the rectifier would have been an option to pass some heat to the filter cap saddle.
Mica is the least expensive type insulator and why do you think they used them. They are not the best to use and when dealing with transistor mounting I usually get rid of them and put a much better Silpad or higher grade interface insulator in there. Do some research on materials that are used for insulators. A lot of amateur or hack shops take a transistor off and drop the mica insulator into the machine and then put nothing back there and you can imagine their result when they do this kind of work but I have caught them. On products that need real good heat conduction like processors there was a substance called Arctic Silver and then Ceramique as pastes to use but they go onto head sinks that are isolated which most
computer heat sink fans are not attached to the chassis.
computer heat sink fans are not attached to the chassis.