Ok, i was browsing a classified board and found a nice Threshold s350e Amp for sale and in looking at the photo's i noticed an interesting heatsink arraingment that brought me back to my original question i posted here some time ago....
If you look at the attached photo. you will see that the TO-3 output transistors are mounted with the tops of the cans away from the outside of the heatsink on a plate of some sort that mounts to the large external heatsinks. presumably with the wiring is between this plate and the heatsinks.
Now in my previous post, i asked why i couldnt mount my transistors to a flat plate bolted between 2 large heatsinks.
So i am curious how this was done in the 350e
Mr. Pass if you have a moment...
Zero
If you look at the attached photo. you will see that the TO-3 output transistors are mounted with the tops of the cans away from the outside of the heatsink on a plate of some sort that mounts to the large external heatsinks. presumably with the wiring is between this plate and the heatsinks.
Now in my previous post, i asked why i couldnt mount my transistors to a flat plate bolted between 2 large heatsinks.
So i am curious how this was done in the 350e
Mr. Pass if you have a moment...
Zero
Attachments
Mr. Zero:
I would think that as long as the trace / wire lengths were kept very short, either way would work. I only post this stab at an answer because I have been informed that Mr. Pass is very busy working on an imprtant new project and may not be available for a speedy reply to your post.
-Casey Walsh
I would think that as long as the trace / wire lengths were kept very short, either way would work. I only post this stab at an answer because I have been informed that Mr. Pass is very busy working on an imprtant new project and may not be available for a speedy reply to your post.
-Casey Walsh
Whenever you are mounting TO-3's on a big flat plate and then
attaching heat sinks to that, there are 3 ways to go that I have
commonly seen:
1) Mount the heat sinks with a gap between the heat sinks which
leaves room for the transistor can to mount from the outside of
the amp.
2) Make a set of spacer bars which create a gap between the
big flat plate and the heat sinks. This spacer must carry the
heat from the plate to the sinks.
3) Use a big extrusion which has the gap of (2) molded into it.
Threshold uses #2, and PL uses #3.
attaching heat sinks to that, there are 3 ways to go that I have
commonly seen:
1) Mount the heat sinks with a gap between the heat sinks which
leaves room for the transistor can to mount from the outside of
the amp.
2) Make a set of spacer bars which create a gap between the
big flat plate and the heat sinks. This spacer must carry the
heat from the plate to the sinks.
3) Use a big extrusion which has the gap of (2) molded into it.
Threshold uses #2, and PL uses #3.
IS it possible to have too large of a heatsink for mosfets? or is it ok to go with the biggest heatsinks you can find?
I understand they need to be rated in c/w at least large enough for said design, but is there such a thing as having too big a sink?
Are there detrimental effects in doing so?
Ie: if we had a 20 watt class A amp and we mounted the the Mosfets to a piece of extrusion being 4' long 12" wide with 3" deep fins, or soemthing else thats way overkill for said design would there be detrimental effects???
Zero
I understand they need to be rated in c/w at least large enough for said design, but is there such a thing as having too big a sink?
Are there detrimental effects in doing so?
Ie: if we had a 20 watt class A amp and we mounted the the Mosfets to a piece of extrusion being 4' long 12" wide with 3" deep fins, or soemthing else thats way overkill for said design would there be detrimental effects???
Zero
spacer plate
would it not be possible to mount the output devices straight to the spacer plate, and isolate the plate from the heatsinks ?
The thermal resistance from the Fets to the spacer would be significantly lower, the heat taken much faster to the heatsinks.
Given a large contact area of the spacer plate to the heatsinks the area of the isolation would be of the same order, creating a small thermal resistance.
Silicon sheets of ample dimensions are available.
Leaves the question of the effects of a potential on the spacer plate ?
jacco
would it not be possible to mount the output devices straight to the spacer plate, and isolate the plate from the heatsinks ?
The thermal resistance from the Fets to the spacer would be significantly lower, the heat taken much faster to the heatsinks.
Given a large contact area of the spacer plate to the heatsinks the area of the isolation would be of the same order, creating a small thermal resistance.
Silicon sheets of ample dimensions are available.
Leaves the question of the effects of a potential on the spacer plate ?
jacco
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