Eeyore said:
The 2N2222 is in TO-18 not TO-39. TO-18 is not a useful package for power
applications.
The fact that the 2N2222 in TO-18 is only good for 500mW whilst the PN2222 is good
for 625mW DESPITE the 50C lower Tj only shows how poor the TO-18 can performs
thermally.
If you make a serious attempt to heat sink the TO-18, I
think you can push it harder than you can by heat sinking a
TO-92. I have seen a few TO-18s soldered to a copper plane,
or into a large plated through hole, or clamped into large
aluminum heat sink, and those could get rid of considerable
power. This was in old equipment where the choices were
TO-18, TO-39, TO-66 or TO-3. Unfortunately, this adds a lot
of capacitance to the
collector node. I think the TO-18 may even outperform the
TO-39 if properly heat-sinked, if the can construction is
the same in each (not the thick base version of the TO-39).
Heat sinking a TO-92 through the epoxy case
has a higher thermal resistance than metal to metal contact,
but at least, provides isolation between heat sink and
collector.