27 Oct
2025
27 Oct
'25
7 a.m.
On Oct 27, 2025, at 6:26 AM, Christian Corti via
cctalk <cctalk(a)classiccmp.org> 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.
Does it mean that a failing PDP-8 will stay a dead PDP-8 from now on?
Christian
Have you tried with an ordinary switching transistor that's readily available?
I'm surprised at that storage time, why would it need to be that low for a machine
that runs at just a couple of MHz?
paull