[MisterX]

You don't want to go much thicker then an 1/8" because you are going to have a very hard time mounting the transistors if you do.

What I did is bought a 6' piece of 2" x 2" stock from Ebay and had the seller cut it into lengths (which he did for free) and then cut the PCB "mounting side" to size with an abrasive disk in my dremel, laid a circuit board over the stock, marked the hole locations, zapped it with the automagic center punch then drilled the holes.
Took about 10 minutes to make each bracket.
(I made 3 sets of heatsink mounting brackets for less then $10)

Unfortunately I cannot locate that ebay seller so maybe try online metals instead?
Order Aluminum 6061 Angle in Small Quantities at OnlineMetals.com

 

[bhjazz]

Quote:

Originally Posted by digger945 /img/forum/go_quote.gif To test the fit I put a drop of oil on the bracket and stuck it to the HS and if it was almost impossible to get the two apart I was satisfied it would work great with just thermal compound.

Very similar to what I've done with CPUs and heatsinks. Better heat transfer = more overclocking!

Nice idea to do it here, digger!

 

[digger945]

Quote:

Originally Posted by Pars /img/forum/go_quote.gif Thanks. Did you buy the L bracket material online or Home Depot, etc.? Same for the carbide blade? I have a radial arm saw, but cutting the brackets would be the biggest problem for me; I have a drillpress, etc. so drilling them and the rest of the work would not be a problem.

Got the aluminum from Ace Hardware, which was a little more expensive than just about any where else, but Ace has a lot of the small fasteners so I got most everything while I was there. The saw is a 10" Makita compound miter(not sliding) from the pawn shop and the blade is a Freud F-40 I think made for wood.


Quote:

As for the mounting hardware, I assume you used probably 4-40 stuff for the output transistors and for mounting the boards to the L bracket? As for mounting the L bracket to the heatsink, I would guess 8-32 from your pics?

Yes the transistor mounting is 4-40 stainless button heads from ebay and/or Fastenal. Started with 6-32 for the bracket to HS mounting but broke 2 drill bits and 1 tap so they ended up being 8-32 with plain socket cap screws/brass washers/rubber washers. I think maybe the rubber washers are not really necessary with Conrads in this particular application. I really didn't know exactly how much heat this beast would make so I just did some guessing.

The key thing for me the next time I do this is to line up the bracket mounting holes so they fall BETWEEN the HS fins. This will make life much easier when drilling/tapping.

 

[Pars]

Quote:

Originally Posted by digger945 The key thing for me the next time I do this is to line up the bracket mounting holes so they fall BETWEEN the HS fins. This will make life much easier when drilling/tapping.

Do the heatsink bracket mounting holes go all the way thru the heatsink, or deadbore into it? From your comment, I would assume this means you are going thru?

 

[digger945]

Yea all the way through as far as necessary to tap the holes. Maybe a bottom tap might work better.

 

[luvdunhill]

Quote:

Originally Posted by FallenAngel /img/forum/go_quote.gif Sorry, I meant "optimal/minimal THICKNESS" to the brackets, not "width". Thanks

basically, the thicker the better, provided you can work with them. There's a tradeoff between using wider brackets (even up to the height of your heatsinks, see some of the Dynamight builds as Digipete did this) and the larger thermal junction. The Cadillac solution is find someone who can bend copper for you.

 

[digger945]

^^Cadillac indeed. I thought about that some in the middle stages of building the Dynamite, just never pursued it much.

I was a little worried about the rather small brackets I used for this build but after it was completed I could see/feel that it was more than adequate for this amp, and I am biased in the lower 90mA range when I should be around 75.

Again what I went with was(from top to bottom):
Transistor
Thermasil III silicon pad, trimmed to fit nice(Mouser # 53-77-9ACG)
1/8" thick 1"X1" aluminum angle, sanded and lapped smooth and the width of the pcb.
I made a jig to bend the legs of the transistors and then assembled/bolted up 2 pcbs(making one channel) and after everything was lined up perfectly, I installed the each channel assembly into the case(the picture I posted above) and tweaked some more until perfect, then carefully remove the 2 halves and solder it up last, after double checking to make sure the outputs are snug.
It took a lot of time to do this

 

[luvdunhill]

Quote:

Originally Posted by digger945 /img/forum/go_quote.gif Thermasil III silicon pad, trimmed to fit nice(Mouser # 53-77-9ACG)

If you have deep pockets, and shop around, you can do better than these. Check out the various ratings of the Bergquist products at Digikey. Other than that, you can make your own using Kapton tape, which perform very well.

 

[digger945]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif If you have deep pockets, and shop around, you can do better than these. Check out the various ratings of the Bergquist products at Digikey. Other than that, you can make your own using Kapton tape, which perform very well.

I will definitely check that out for my upcoming dyna build.

I had to take her apart and change the bias resistors so I snapped a couple more pics to maybe help out.

I will consider using just one long piece of angle for both boards on the next build.

 

[FallenAngel]

Quote:

Originally Posted by MisterX /img/forum/go_quote.gif What I did is bought a 6' piece of 2" x 2" stock from Ebay and had the seller cut it into lengths (which he did for free) and then cut the PCB "mounting side" to size with an abrasive disk in my dremel, laid a circuit board over the stock, marked the hole locations, zapped it with the automagic center punch then drilled the holes. Took about 10 minutes to make each bracket. (I made 3 sets of heatsink mounting brackets for less then $10)

Thanks for the info, just one clarification - by "cut mounting side to size", do you mean down the entire 5' length of the L-bracket? That sounds a little difficult (and time consuming with a Dremel).

I just measured mine to be 1/16" thick and a little worried about that. Likely going with the ones you linked to.

 

[MisterX]

Yes, down the whole length of the bracket and it was actually pretty easy to cut with a dremel once I sat down and did it. Sure did make a mess though.
(if I was going to make another set of brackets today I would use the bandsaw I picked up a couple of weeks ago instead)

Maybe ping the seller from the auction below and see if he will cut them for you?

Aluminum Angle 36" piece 2" x 2" x .125" - eBay (item 200329712685 end time Apr-15-09 19:46:54 PDT)

 

[FallenAngel]

Thanks buddy, good link.

I'm thinking I'll ask to have these cut to lengths. At 1" x 2", it should sit well enough and only stick out by 0.4" so it should be quite manageable. I'll ask if they'll cut short lengths.

Ooh, found this - looks prettier and 0.5" x 1" so it doesn't have to be cut lengthwise, just to board size.

 

[MisterX]

Those are a lot more manageable.
Stoopid.... I looked right at both of them when I was poking around on Ebay and never even thought twice about them.

 

[digger945]

The 1" X 2" looks perfect for me. Very reasonably priced, not bad on the shipping either.

 

[luvdunhill]

nm