Den mån 27 okt. 2025 kl 23:03 skrev Jon Elson via cctalk < [email protected]>:
> On 10/27/25 14:17, Brent Hilpert via cctalk wrote: > > On 2025Oct 27,, at 9:37 AM, Christian Corti via cctalk < > [email protected]> wrote: > >> On Mon, 27 Oct 2025, Paul Koning wrote: > >>> 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? > >> The storage time is very crucial. We have tested many different > switching transistors. The point is, the PDP-8 uses needle impulses (around > 30ns) to switch a flip-flop. They just don't work with today's transistors. > And on modules like the R211/S211, they introduce a too long delay. > > > > Cob, fT not quite as good, but close: > > > > 2N5400: Cob=6p0, fT=400MHz > > 2N4916: Cob=4p5, fT=400MHz > > > > vs 2N3639: Cob=3p5, fT=500MHz > > > The MPSH81 shows Ccb = 0.85 pF and Cce = 0.65 pF and fT 600 > MHz. They don't give a Cob spec. > They actually show the output capacitance in a diagram as a function of reverse bias voltage. Between 0.8 pF and 1.8pF depending on voltage. /Mattis > Jon > >
