Transistor Substitution

Brent Hilpert hilpert at
Wed Jun 10 13:00:40 CDT 2009

Allison wrote:
> >> FYI: Older DEC machines like straight-8 and friends used a lot fo the ceramic
> >> epoxy parts similar to the 2n3638 and 2n3563.
> >>
> >> Those are ceramic headers with
> >> a block of epoxy covering the die and are prone to popping the epoxy and the
> >> symptom works when cold or mechanically intermittent.
> >>
> >
> > Is that visually apparent, or is that an internal fault?  If I
> > identified a bad transistor and removed it from a FLIP-CHIP, would it
> > be difficult to set up something with an oscilloscope to watch some
> > output then tap on the transistor to watch the trace "change" to
> > verify mechanical fragility?
> >
> Its rare to see the top epoxy pop off but it happens.  usually the part
> either fails
> or  is most often thermally intermittent.

TMK, only Fairchild made those packages, although they had JEDEC numbers
(TO-105 and TO-106).

I kind of liked them somehow, perhaps a nostalgia thing. (Never seen them fail
mechanically, myself.) In all sorts of commercial equipment around the mid-60's
to 70's. 2N3638 was very popular.

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