Base resistor

[ericgibbs]

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

Read your edit.

Eric

 

[audioguru]

If a TTL output is high and its connected to a TTL input which requires 1.6mA, where is the current coming from, if not the driving source.???

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.

 

[ericgibbs]

hi audioguro aka U$,

Like you, I 'upgraded' to CMOS and the HEF LOCMOS as soon as they became available, all my commercial marine products were MOS based.

I suspect like me, you cut your teeth on things like 741's, EF50's and EL84's would I be wrong?.

Regards
Eric

 

[Nigel Goodwin]

I suspect like me, you cut your teeth on things like 741's, EF50's and EL84's would I be wrong?.

Only in that EF50 and EL84 are European Pro-Electron numbers, and not really used in North America.

 

[ericgibbs]

hi,

The EF50 was designed by Philips in the 1930's and manufactured during WW2 by Sylvania in North America.

Eric

Edited:Corrected designed by.

 

[Roff]

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

Read your edit.

Eric

Yeah, I'll believe 3.9V with no load, and 27mA when connected to the base, but not both simultaneously.

 

[audioguru]

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.

 

[Nigel Goodwin]

I remember that Philips vacuum tubes were stamped Mullard.

Mullard was the component manufacturer, Philips bought them out a long time ago, and eventually changed the name to Philips Components.