First: the big clincher here is that these JFETs are not close enough to use one of the Xen heatsinks from the group buy a while back.
Let’s say one has 2SK170 / 2SJ174 input JFETs, not exactly next to one another.... maybe a couple cm apart.
I’ve seen the custom heat sink made here for JFETs directly next to one another.
I think this was streamlined by EUVL / xen audio. I checked their site but came up empty handed.
http://www.diyaudio.com/forums/group-buys/135359-toshiba-dual-jfet-heatsink.html
From what I’ve seen they wrap around the sides.
I’ve been able to locate totally circular ones but I am not sure if this would defeat the purpose of not making close contact with the flat side.
I was thinking of using thermal paste and creating a bridge between them. I figured the safest way to accomplish this is by adhering copper shims commonly used for ram dimms to the top of the JFET and then bridging it with a small bar of aluminum. My thinking was copper would aid in absorption, aluminum (possibly with fins from some other transistor package size from mouser) to aid in dissipation. Would this be bad form?
Which side of the JFET gives off the most heat?
Would a heat sink on each JFET minimize effects without need for a bridge?
Has anyone rigged something like this up?
If so, pictures speak a thousand words.
Thanks as always.
Let’s say one has 2SK170 / 2SJ174 input JFETs, not exactly next to one another.... maybe a couple cm apart.
I’ve seen the custom heat sink made here for JFETs directly next to one another.
I think this was streamlined by EUVL / xen audio. I checked their site but came up empty handed.
http://www.diyaudio.com/forums/group-buys/135359-toshiba-dual-jfet-heatsink.html
From what I’ve seen they wrap around the sides.
I’ve been able to locate totally circular ones but I am not sure if this would defeat the purpose of not making close contact with the flat side.
I was thinking of using thermal paste and creating a bridge between them. I figured the safest way to accomplish this is by adhering copper shims commonly used for ram dimms to the top of the JFET and then bridging it with a small bar of aluminum. My thinking was copper would aid in absorption, aluminum (possibly with fins from some other transistor package size from mouser) to aid in dissipation. Would this be bad form?
Which side of the JFET gives off the most heat?
Would a heat sink on each JFET minimize effects without need for a bridge?
Has anyone rigged something like this up?
If so, pictures speak a thousand words.
Thanks as always.
You want them to be at the same case temperature, but different physical locations,
as well as convection currents, prevent this. An aluminum or copper bar between
their flat faces helps, but mounting them close enough to clamp their flat faces
together with thermal paste is best.
You can't prevent convection currents, if things are at different temperatures. Hence you have minimise the differential effects of convection currents by ensuring the two transistors are close together and well-coupled thermally.
The sensitive parts can be close together in a small board-mounted enclosure (oven).
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