hi,
The point that puzzled me was the +3.9V at pin12 while driving 27mA into the
transistor base. It should be lower than 3.9v, as the Vbe on the transistor is around 0.7v
Hi Eric,
I haven't looked at old TTL for many years. I like Cmos logic ICs ever since they were introduced in about 1968.
The input of TTL pulls itself high, but slowly. A TTL output supplies current when it goes high to quickly charge the input and wiring capacitance of the input it is driving.
I think the input that is at a logic high is sourcing a small current to the output that quickly allowed it to go to a logic high.
hi,
The point that puzzled me was the +3.9V at pin12 while driving 27mA into the
transistor base. It should be lower than 3.9v, as the Vbe on the transistor is around 0.7v
I knew about some of the European parts from reading Wireless World (British) magazines. I can't remember which vacuum tubes were in my Heathkit amplifier but they were marked with both the American and the European numbers.
I remember that Philips vacuum tubes were stamped Mullard.
He used an 'LS TTL IC which has a different circuit than an ordinary TTL IC. The output voltage of an 'LS goes to a higher voltage than an ordinary TTL IC.
When the base-emitter voltage of a little NPN transistor measures 3.9V then it is busted.