TTL to NIM logic translation Logic Gate Issue
I'm not sure how that worked even with the original 'F86 gate &mdash; it has a specified maximum IOH of -1 mA.

In any case, I would recommend ditching the gate altogether and using another differential amplifier for input.







simulate this circuit &ndash; Schematic created using CircuitLab

Q2, R3 and R4 establish the switching threshold for the TTL input. The rest of the circuit is the same as your reference.

If you still want switchable polarity, connect the 'x86 gate to the TTL in shown here.