tube dc hum
Hello Thomas,
I don't understand, what is working now.
1. The "ground" is identical to -3 V, so you have arround 5 V supply at the TTL/HC/whatever IC (564 pin20, 7420 pin 14)
2. The switch operation should be such, that 564 pin 2,3,4 have high idle level and
go to low each, when the corresponding switch is pressed.
3. 7420 pin 6 has idle state high and goes low, when any switch is pressed.
I think, the 1k resistor at pin 11 should be a pull-up to positive supply, not a pull-down to ground. Then the switch state would be latched 100 ms after pressing the switch. Now it is latched on release, but depending on the different logic IC threshholds possibly too late.
May be the second drawing error with the schematic.
Regards,
Frank