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How do you mount your transistors ?
How do you mount your transistors ?
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Old 7th May 2002, 03:16 PM   #21
Peter Daniel is offline Peter Daniel  Canada
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If you are mounting TO-3 transistors the best way is to use L or U bracket so you don't have to use nuts on the heatsinks.
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Old 7th May 2002, 03:57 PM   #22
Lisandro_P is offline Lisandro_P  Argentina
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Quote:
Originally posted by lordvader
You insulate the transistors with grease, a washer, whatever, but then you screw them down. A screw is made of metal, and it makes contact with the transistor AND the heatsink. Wouldn't that defeat the purpose of insulating in the first place?
There's to ways (i'm aware of atleast) to overcome this. The first one is to use a special plastic "washer" that isolates the heatsink from the screw through it. You place it on the heatsink screw hole and it covers the top and the inside, so the screw floats at the voltage of the transistor but the sink is isolated from it. I use them all the time and never had a problem.
The other one is nylon nuts and screws. Yes, they do exist and are relatively cheap (not as much as the washer thing through), but i had my problems with them... if you, for whatever reason screw and unscrew them a couple of times the threading on the screw just ruins.
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Old 7th May 2002, 05:14 PM   #23
vpharris is offline vpharris  United States
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Default Re: Screw & Nuts

Quote:
Originally posted by chris ma
HPotter,

Where do you get your hardwares normally? I have so much frustration trying to get some screws and nuts in Toronto. I tried home depot, canadian tire, sayal, active surplus etc.. either they have the screw but out of stock with the nuts or washers. Or they do not have the right length.
Chris
You see that your neighbor HPotter gets his at Home Depot. You could also try a marine store, since you're in a waterfront town. They should have lots of choices from #6-#12, pan head and FH, at least. Also, go to McMaster Carr (online). They have everything, though perhaps not one screw at a time. They ship same day, and you'll have them in 2 days. Not bad.
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Old 7th May 2002, 06:08 PM   #24
Peter Daniel is offline Peter Daniel  Canada
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I don't know if you checked there but Canadian Tire has a really good selection of fasteners. Check the racks in hardware section.
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Old 7th May 2002, 07:04 PM   #25
chris ma is offline chris ma  Canada
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Default Nuts

I have tried both Home Depot and Canadian tire, they have only big ones not the ones to mount the TO-3, TO-220 on heatsinks,
even for PCB standoffs are too big too..

Also I am looking for some small thru PCB mount terminals (can be tighten by the nut on top of PCB) so that I can remove all the external connections in order to take the PCB out of the chasis without desoldering for parts replacements. For example where the PSU PCB connects to Amp PCB as well as all heavy ground wire connections to star point etc..

Thanks for the suggestions,
Chris
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Old 7th May 2002, 08:50 PM   #26
Peter Daniel is offline Peter Daniel  Canada
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Try Sayal Electronics at 1350 Matheson Blvd E. Unit 3, (905)238-8640. They have almost everything. And Home Depot has #6-32 screws.
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Old 7th May 2002, 09:27 PM   #27
Petter is offline Petter
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Default I recommend ....

Due to the problem of using the right amount of grease (usually too much is used + the best types are too thick to work with), I recommend going greaseless. I ended up using Bergquist Silpad 2000 which guarantees very high performance.

For best electrical, capacitive and thermal performance, go with BeO types (you still have to contend with the grease problem which can reduce thermal performance significantly). BeO has another problem -- while harmless in it's fired state, ground up dust is toxic and leads to berylliosis if inhaled. This is similar to Astbestosis which is the effect of Astbestos. Strange how materials so dissimilar in thermal property have virtually identical effect on the body. BeO also has interesting radiological properties.

Some people like Aluminium Oxide washers (misnomer -- they are Aluminium which has oxide layer on both sides). These should also perform well IF you mount them properly, but do not have the same fantastic dielectric properties as BeO.

Save yourself the trouble and mess and go with Silpad.

As for mounting instructions and torque, the Aavid/Thermalloy site has a good white paper on this per package type -- incidentally they are also the only manufacturer of BeO type washers I have found to date.

Petter
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Old 9th May 2002, 01:32 PM   #28
chris ma is offline chris ma  Canada
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Default #6-32 screws

I bought all stainless steel #6-32 screws, nuts, washers, split ring etc.. just to get more frustrated when I got home, the #6 screw can not even go thru the Caddock resistor's mounting hole, and it is too big for the heat sink hole too! I think I'll have to find some shop that sells 3mm screws and nuts, I tried Sayal last weekend they have the 2.6mm 2.8mm and 3mm screws but no washers and nuts, have to wait for the next shippment....
No joy.......My mistake, I should have carry the heatsink and the resistors with me all the time..the I save a few dollars.

The other problem I have also is the capacitor mounting clamps. It was so funny when the guy at the shop try and bend those clamps and convince me they will fit my caps that I brought and show him. Now I'll have to buy those clamps from UK too and pay shipping, custom brokerage and import duty too for some simple hardwares ! It is a joke that this industry in Toronto is in such a state!
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Old 9th May 2002, 02:14 PM   #29
Sidney is offline Sidney
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Rod Elliott has a very informative article at his web site.

http://sound.westhost.com/heatsinks.htm

I've used his mica washer splitting technique and it makes a significant difference in heat transfer
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Old 9th May 2002, 02:32 PM   #30
Peter Daniel is offline Peter Daniel  Canada
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Chris,
What project are you working on?
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