Hero999 said:
That's nonsense, I've built and run an astable multivibrator for hours from 9V when I was about 12 and it didn't damage the transistors.
If you're lucky, and you happen to use transistors suitable, you 'may' survive at 9V - increasing to 12V makes it pretty certain to die.
If you were flashing LED's in the collectors bear in mind this also drops the supply by their forward voltage drop.
I first came across this at college, where we were split in to two teams to build a simple 'one armed bandit' from a block diagram. The project had been knocking around for years, but they had never had a group capable of it.
In the end the two teams were amalgamated, with me and another guy doing most of the work - one of his tasks was to build three astable multivibrators. And despite the fact I repeatedly told him, even showing him the reason in a book from the library, he kept blowing the transistors in them. In the end he had a pile of 50-60 dead transistors, but managed to find six that survived in his astables! - this same guy actually became a teacher at college later on!.
For anyone interested, the project was three 7 segment displays (incandescent - long before LED's), using just the horizontal segments. You had to stop the changing segments in a straight line, using a stop button on each.
It consisted of:
3 x astables (one for each channel)
3 x bistables (for the stop buttons)
3 x ring of three counters (for cycling the displays)
3 x drivers and displays
Logic gating to drive a WIN/LOSE light.
This all had to be built using just discrete components (it predated IC's really anyway, although I think RTL was out?), each module had to be built on a seperate matrix board, with all components and wiring on the top surface. The entire device was built under a perspex cover so visitors on open day could see the internal workings, and play the machine.
If most people haven't heard of a 'ring of three counter', neither had we back then!
I went to the library and found out about them in a book!.