Uncle $crooge,
I'm beginning to understand. You are concentrating 4 of the components, ignoring the other 9 in the schematic.
The datasheet for 1N4148 has a max Forward Voltage, V(FM), or 0.715V. The datasheet for BC557 has a max Base-Emitter On Voltage of -750 mV.
Is that where your 0.7V came from?
On the NTE30001 datasheet, the High Output is at I(F) = 20 mA. Is that how you chose the 27 ohms?
If so, how did you (how would I) know to ignore the rest of the schematic, to see if the resistor should be 180 ohm or 30 ohm? At this stage in my understanding, I would have thought I needed to account for all 9 volts.
Thanks a lot.