10 Nov
2025
10 Nov
'25
12:22 a.m.
On Sat, 8 Nov 2025, Tom Hunter wrote:
I got hold of some MPSH81. Unfortunately they are not
a suitable substitute
for a 2N3639 or 2N3640.
[...]
Well, the datasheet say that this is an RF transistor, it is per se
unsuitable for on-off switching into saturation.
"This device is designed for general RF amplifier and mixer applications
to 250 MHz"
The datasheet for the MPSH81 doesn't even specify
tON, tOFF and tS, but the
fT of 600 MHz appeared promising.
fT is not really important. That tON and tOFF are not specified is normal
for RF-only transistors. You need to look out for "high-speed
staturated switching" applications in the datasheet.
Christian