I'm building an amp from scratch using Exicon TO3 transistors for the outputs, all mounted to a thick heatsink. I have the install kits for each one with socket and thin plastic gasket. My questions:
- Should I drill one large hole for both the TO3 leads to pass through the heatsink, or should I drill two smaller holes?
- I'd like to use heat sink compound, what's the proper order of all the the mounting kits parts (T03, spacer, compound, heatsink, etc) when installed?
- Should I drill one large hole for both the TO3 leads to pass through the heatsink, or should I drill two smaller holes?
- I'd like to use heat sink compound, what's the proper order of all the the mounting kits parts (T03, spacer, compound, heatsink, etc) when installed?
Hi,
drill 4 holes for the To3.
Two for the mounting bolts and insulating top hats. Two smaller holes for the base and emitter leads.
If you can, make a drilling jig for the To3 layout. Preferably in steel to give sufficient life. Clamp it into place and drill your holes. They must be accurately located to ensure the semi casing bolts up correctly and that the leads do not short if bent slightly out of alignment.
The edges of the holes must be deburred to ensure the raised surface does not puncture the mica insulation.
The mica washer must be coated on both sides with thermally conductive paste, not silver loaded paste which is electrically conductive and can short the collector to the heatsink.
The assembly order is heatsink - paste - mica - paste - To3 - tophats - bolts - nuts.
One or both of the nuts should have a copper or tinned copper tag to connect the collector to the rest of the circuit.
drill 4 holes for the To3.
Two for the mounting bolts and insulating top hats. Two smaller holes for the base and emitter leads.
If you can, make a drilling jig for the To3 layout. Preferably in steel to give sufficient life. Clamp it into place and drill your holes. They must be accurately located to ensure the semi casing bolts up correctly and that the leads do not short if bent slightly out of alignment.
The edges of the holes must be deburred to ensure the raised surface does not puncture the mica insulation.
The mica washer must be coated on both sides with thermally conductive paste, not silver loaded paste which is electrically conductive and can short the collector to the heatsink.
The assembly order is heatsink - paste - mica - paste - To3 - tophats - bolts - nuts.
One or both of the nuts should have a copper or tinned copper tag to connect the collector to the rest of the circuit.
Two follow up questions.
1. What is a good brand (or composition) of paste?
2. Without referring to a torques wrench settings, about "how much" force should be used to tighten the fasteners? IOW, not so much that it would deform the case, yet enough to ensure proper thermal conductivity. I am not sure how one communicates that in words.
Thanks
1. What is a good brand (or composition) of paste?
2. Without referring to a torques wrench settings, about "how much" force should be used to tighten the fasteners? IOW, not so much that it would deform the case, yet enough to ensure proper thermal conductivity. I am not sure how one communicates that in words.
Thanks
Hi reiver
How are your outputs arranged? Are they along one edge of
the board or are they along opposite edge of the board? Or are you 'flying' leads from the board to them?
Four holes will be easier for you to do because if you are making 1 big one for the B,E, that would be a huge (presumably you can make only circular holes with your drill) one Expect to make a mess with the compound, its quite difficult to clean up after you mounted them. Have fun with the after-play.
If you try to 'google' your title, there should be some nice drawings showing you exactly how to do it.
How are your outputs arranged? Are they along one edge of
the board or are they along opposite edge of the board? Or are you 'flying' leads from the board to them?
Four holes will be easier for you to do because if you are making 1 big one for the B,E, that would be a huge (presumably you can make only circular holes with your drill) one Expect to make a mess with the compound, its quite difficult to clean up after you mounted them. Have fun with the after-play.
If you try to 'google' your title, there should be some nice drawings showing you exactly how to do it.
re:
I'm creating a Hafler xl280 copy, with 3 N Exicons on one heatsink and and 3 P Exicons on the other. I'll be daisychaining the wiring to mimic the wiring on the original Halfer so it should be fairly easy.
I have a use generic amp arriving in a couple of days, so I'm not sure 'exactly' what the heat sink will look like. I's going to be a very fun weekend though....
I'm creating a Hafler xl280 copy, with 3 N Exicons on one heatsink and and 3 P Exicons on the other. I'll be daisychaining the wiring to mimic the wiring on the original Halfer so it should be fairly easy.
I have a use generic amp arriving in a couple of days, so I'm not sure 'exactly' what the heat sink will look like. I's going to be a very fun weekend though....
The heatsink I'm using is flat on both sides where the mosfets sit, with ribs father down the sink. So I should be able to mount them solidly, I think I'll just use a template and scribe the holes before drilling.
If I drill carefully and make the B/E lead holes slightly oversize I think it will work out ok.
-Bryan
If I drill carefully and make the B/E lead holes slightly oversize I think it will work out ok.
-Bryan
another caveat. if you are using mica washers or sil-pads.... make sure the heat sink is smooth with no burrs on it, especially around the mounting screw hole. also watch out for aluminum shavings that can easily poke a hole through your insulator and cause a short from the transistor collector to the (usually grounded) heat sink.
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