Re: TO-5/TO-39 Heat Sinks -- How tight a fit is needed

From: colin (no.spam.for.me_at_ntlworld.com)
Date: 07/20/04 

Date: Tue, 20 Jul 2004 14:29:40 GMT

"Norm Dresner" <ndrez@att.net> wrote in message
news:GXSKc.283858$Gx4.81000@bgtnsc04-news.ops.worldnet.att.net...
> For a special project, I'd like to use paralleled TO-5/TO-39 transistors
in
> the output of a moderately low power amplifier -- say 15W -- much like is
> done with TO-3 and TO-220 transistors for high-power amplifiers. The
> intent is to get a higher slew rate and wider frequency range with the
> faster transistors available in the smaller size cans. There are
probably
> a few TO-202 types I could use but the TO-5/TO-39 are more common and have
> higher Ft and gain for less price, though in a 1-4 unit production for
> internal use that's hardly a consideration, but I have to keep it
reasonable
> (i.e. under the radar).
>
> In order to insure the best thermal tracking of the output, I feel I need
a
> common heatsink for each polarity of the output drivers separately (using
> complementary feedback output stage topology). But to do this, the only
way
> I can think of is to take a massive piece of aluminum and drill holes for
> each transistor case to fit in. Drawings I've found give the diameters as
> TO-5 .320" +-.015"
> TO-39 .325" +-.010"
>
> If I drill holes that are .328" (21/64 IIRC), I'd pretty much be at the
> nominal diameters for both sizes but the TO-5's could be as much as .023"
> smaller than the holes. My intuition says that's too much for a good fit
> for efficient heat transfer but I have absolutely no experience in this
> regard and I'm hoping that someone else would know. I also have no
feeling
> for how hard or easy it would be to force oversized cases into unyeilding
> holes.
>
> Information and alternate suggestions appreciated.
>
> TIA
> Norm
>

im reminded of a philps signal generator wich i looked inside long time ago
and at the circuit and found it had a nice output stage just consisting of
several TO5s think they were something like 2n2219/2n2905. might be a good
place to get design idea.

Colin =^.^=