Thermal management

[Linear Purpose]

In solid sate amplifier thermal management is a critical point for performance an reliability.

Nevertheless it is often an under estimated part of the design.

For example there is still people using MICA insulators (which are completely obsolete) between transitors and dissipator ...

There is certainly lots of ideas to share on that subject !

 

[CBS240]

...For example there is still people using MICA insulators (which are completely obsolete) between transitors and dissipator ...

Mica is obsolete My mica insulators work quite well if you mount them properly. There may be material out there that works a little better but when you factor in the price...
You just have to deal with the heatsink grease.

 

[AndrewT]

Mica insulators conduct heat better than many of the new insulators that are marketed.

The main purpose and reason for these "dry" insulators is to save assembly time.

 

[whoandcar]

"It is not a disgrace to fail. Failing is one of the greatest arts in the world."

I usually fail with complete succes...

 

[wg_ski]

By far the best way is to mount the transistors directly to the heatsink, but that creates other headaches. You either have to run the sinks electrically hot or limit yourself to a grounded collector topology.

 

[Dr_EM]

The mechanical mount is important too. Using Hex head bolts will help and ideally a clamp can be used (again tightened with hex type bolts). For insulators I tend to use Sil-Pads, seem to work pretty well (had a heatsink untouchably hot in one test setup but the chips never cut out or had problems).

 

[EWorkshop1708]

I use wide clear tape on my heatsinks, so far success and no issues.

I stick the tape on the heatsink, making sure of no air pockets, and grease the transistors, and stick them to the tape, and clamp them down. The thermal performance is good.

I'm not worried about melting the tape, because if I run it that hot, which I doubt, then I have more problems to worry about than the tape anyway.

 

[MJL21193]

My first time I was impatient to try my creation and I used thermal grease and paper. Ordinary white printer paper cut to size. Amp had 56V rails, and it worked fine.

I later changed to mica to be on the safe side.

 

[jrockhead]

For example there is still people using MICA insulators (which are completely obsolete) between transistors and dissipator ...

Obsolete??? I would not use anything else. As others have stated and I verified for myself the other types have worse thermal performance than mica and good thermal grease.

 

[EWorkshop1708]

My first time I was impatient to try my creation and I used thermal grease and paper. Ordinary white printer paper cut to size. Amp had 56V rails, and it worked fine.

I later changed to mica to be on the safe side.

Wow, you used paper???

At least you greased it though. That thermal grease is great stuff.

I saw a car amp one time someone tried to fix, and they put pieces of fairly thick paperboard behind the transistors with no grease

Here's a heatsink I just done with clear tape. You can hardly see the tape with the naked eye

 

[MJL21193]

Wow, you used paper???

Here's a heatsink I just done with clear tape. You can hardly see the tape with the naked eye

Yeah, the good old days (last year?? ).

I like the tape idea. Regular clear packing tape? Certainly more convenient.

 

[CBS240]

I usually fail with complete succes...

An easy skill to master.





It really is the grease and it's liquid state. Even if the mica has been bent and has a fold in it, use an even coat of grease to fill in most of the pits and valleys of the metel and mica, and it still works better than some of those grease-less pads. Paper...

 

[EWorkshop1708]

Yeah, the good old days (last year?? ).

I like the tape idea. Regular clear packing tape? Certainly more convenient.

Correct, packing tape like what's regularly used to tape boxes instead of heatsinks It kinda looks like mica anyway, so I figured it would make a good substitute. And for $1.50 a roll, not only is it easy, but it's also inexpensive.