27 Oct
2025
27 Oct
'25
8:16 a.m.
On 10/27/25 05:26, Christian Corti via cctalk wrote:
It seems that nowadays you can't get *any*
replacement for
failing DEC 3639 aka 2N3639 transistors. All parts are
obsolete and unobtanium, e.g. 2N3640, PN3640, MMBT3640 and
so on.
So, what can be used instead? The most important
electrical parameter is the storage time. It needs to be
*very* low, around 20-30 ns.
I saw a data sheet that mentioned an MPS3639. But, I didn't
find a distributor that had these, either.
Possibly not a direct substitute due to pinout, but the
MPSH81 is a very fast, low-capacitance PNP transistor. I
have used it to replace germanium PNP transistors in some
gear. Just a total drop-in replacement, didn't need to
touch the bias network.
Jon