Senior Member
Joined: 11/12/2020
Location: AustraliaPosts: 122
| Posted: 11:12am 15 Jan 2023 |
a back to back zener diode.
it would limit the voltage that the base of Q7 is exposed to from pin 3 & pin 4
you would probably need to go back to scanned copies of old parts catalogs to find them.
its probably easier to experiment & start with sum 6v zeners