Bill,
Only use mica or the various pads if you require electrical insulation.
They do not conduct heat anywhere near as effectively as the thermal grease
by itself. If you do require electrical insulation (maybe the case of the
transistor is one of the leads and you cannot insulate the heat sink itself
from everything else) then you have no choice.
In such cases what we do if we are using aluminum heat sinks is we send them
out to be black anodized first. This anodize is an excellent electrical
insulator and an excellent heat conductor. Just be careful not to scratch
it.
Regardless of which method you use, if you chill the heat sink using an a
TEC, the whole package will handle far more heat.
Gary
----- Original Message -----
From: "Bill Acito W1PA" <w1pa@hotmail.com>
To: <TenTec@contesting.com>
Sent: Wednesday, March 07, 2007 10:31 AM
Subject: Re: [TenTec] Is there a beefier 2N5301?
> Thanks to all that commented.
>
> Plan of action will be:
>
> Replace the current pass transistor with an NTE181 (not cheap, about $6 at
> Jameco),
> but has the best combination of power handling and break down voltage
(30A,
> 100V, 200W).
> It appears, based on a quick search of the archives, that TenTec actually
> used these as well.
>
> The 2N5302 ($2 at Surplus Sales of Nebraska) is 30A, 60V, 200W
>
> Googling "TO3, NPN, 50A" found a 2N5686 (50A, 80V, 300W) and 2N6277
> (50A, 150V, 250W) with similar gain (hfe 15-60) but
> I'm not enough of a circuit guy to tell what they might do as a
replacement
> from the data sheet. And as we discussed, if the heat
> sink isn't cutting it, there is no sense in moving up to a "bigger"
device.
>
> Thanks for the comments on the thermal grease -- I do tend to go to heavy
on
> this stuff. Also, the
> last time I replaced one, mica was the TO3 insulator of choice. Should I
> move to the new "gray pad"
> material, versus the mica/grease combo?
>
> I also plan to add a quiet 12v fan to the heatsink, and we'll see how it
> goes.
>
> Bill
> W1PA
>
> _______________________________________________
> TenTec mailing list
> TenTec@contesting.com
> http://lists.contesting.com/mailman/listinfo/tentec
>
>
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