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Jens Rasmussen Leach clone group buy

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#1,261
Sholder Washers...........

Actually the transistors do use a shoulder washer. (see photo) The #4-40 screw is too small for that transistor. It all fits just right with the part number previously given.
 

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#1,265
I would like to know if anyone has found a TO-264 insulator? The Al-oxide pads (4180G) just fit the die area under these transistors
Click to expand...

I found these insulators at Mouser: P/N:567-175-6-280P. Cost is only 32 cents a piece(half that of the Al-Ox). I believe these will work fine as well.

Attached is a photo of one applied to a 4281.

-Chas
 

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#1,267
Thew following is a good read and may help other "newbies" out there to have a more complete understanding of the concept:

http://sound.westhost.com/heatsinks.htm#7

The many cautions about the Al-Ox pads being fragile concern me, as I personally don't have a precision torque wrench. The 0.006" Kapton pads(shown above) or Sil-Pads may be easier for the first-timer.

My group of builders has chosen to use a very thin (.0015") adhesive Kapton tape, with application of thermal compound on the "dry" side, since our heat sinks are relatively flat and smooth.

-Chas
 
#1,268
clm811 said:

My group of builders has chosen to use a very thin (.0015") adhesive Kapton tape, with application of thermal compound on the "dry" side, since our heat sinks are relatively flat and smooth.

-Chas
Click to expand...

Not sure this is the same Kapton tape recommended by Bob, I am using those in my Alpeh. They worked beautifully. Of course, a little Artic Silver compound in between the transistor and the tape 🙂

I also used the transistor clips/springs recommended by Bob. They really hold the transistors onto the Kapton tape tightly, yet without worry about over torque. Needless to say tapping 6/32 is much than the 4/40.

Kudo to Bob on both counts!!
 
#1,271
Don't have the thermal resistance of the Al oxide spacers at my fingertips, but it was mentioned in another thread that they pose less of a capacitance between the transistor and heat sink, which capacitance was suggested as being detrimental.

Also, the Al oxide pads are thicker, which can space the transistor farther from the heat sink. So if the pad does not accurately cover the transistor, there could be less of a chance of shorting to the heat sink.
 
#1,272
Pooge, that makes me feel better better about the purchase. Not sure what the capacitance issue is, but it won't be causing me a problem

Aavid now lists the part as TO-3P compatible, and the fit really is fine.
Chas is suggesting a precision torque wrench, which I don't have :xeye:
I need a Smiley that rolls dice...
 
#1,273
pchw said:
I also used the transistor clips/springs recommended by Bob. They really hold the transistors onto the Kapton tape tightly, yet without worry about over torque. Needless to say tapping 6/32 is much than the 4/40.

Kudo to Bob on both counts!!
Click to expand...

Hi Fred
I was interested in the clips. Do you think they would be compatible when using Al-Oxide pads that add 2mm/.08" to the TO-264 package height?
 
#1,274
Don't know if clips would provide the best amount of pressure. They would certainly work, as that is what they are designed for. But proper torquing of a screw would more than likely give you more pressure and less thermal resistance. It would behoove you to at least buy, borrow or rent a torque wrench for this purpose, though. Or you could just drop by a mechanic and ask him to torque them for you. By getting the proper torque, you are maximizing the pressure, yet being careful not to apply so much as to crack the transistor case or raise the surface of the heat sink around the screw, which would cause loss of contact between the transistor and sink.
 
#1,275
rob3262 said:


Hi Fred
I was interested in the clips. Do you think they would be compatible when using Al-Oxide pads that add 2mm/.08" to the TO-264 package height?
Click to expand...
Hi Rob,

I will take picture of the clip when I go home after work, I will also use the Al-oxide pads along the kapton tape so that you can see how the clip works on both. It will be evening Pacific time.

Cheers,
 
#1,276
Not sure this is the same Kapton tape recommended by Bob...a little Artic Silver compound in between the transistor and the tape 🙂
Click to expand...

Fred,
I'm referring to the same tape(3M#5413) that you bought through eBay(from the specs, the total thickness is actually closer to .0025", due to the adhesive).

BTW- thanks for buying the tape!

-Chas
 
#1,277
#1,278
I have used this same approach (clips + Kapton tape) in the past with good results.

These are similar similar clips I bought on eBay for almost nothing. 😀

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#1,280
sping clips

tough call. For TO-264 with oxide spacer, it looks like there is a loss of mechanical leverage. I find myself in agreement with pooge, that screwing the transistor directly to the sink will likely exert more force, resulting in better themal performance. Again, tough call without actually trying these clips myself.

Duda, you're satisfied with the amount of force the clip imparts?

Fred, that sink is waiting to be drilled & tapper for leach? I see a lot of holes all over the place...
 
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