On 2025-10-27 8:00 a.m., Paul Koning via cctalk wrote:
On Oct 27, 2025, at 6:26 AM, Christian Corti via cctalk <[email protected]> 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? ChristianHave 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
The 20 Mhz time state generator in some PDP 8's just kills that idea. Ben.
