NIM is a standard used in nuclear physics. I'm facing an issue with a logic gate being used in my TTL to NIM translation circuit, and I'm not sure what is entirely wrong with it. For a little background, I'm trying to replicate a TTL to NIM logic translation circuit as demonstrated in a reference schematic linked below, but I'm having some issues regarding a specific part of the circuit, specifically the logic gate.
It's a little modified from the original circuit with the addition of a pull-down resistor at my TTL logic input at the gate as well as using 5 pF capacitors instead of 3.3p, but otherwise, the rest are the same.
The original schematic used an XOR gate, and it seems to be the F86 XOR gate. I used the 74LS386 quad dual-input XOR gate to substitute for it, but it doesn't seem to be working properly. Setting one input to ground, I used a switch to set the other input to 3.3 V for the TTL high input (and when the switch is open, a pull-down resistor for that input pulls it down to 0 volts for logic 0). The output of the gate goes to the rest of the circuit, which should produce a NIM-logic current signal (0 mA for logic 0, -15 mA for logic 1). However, somehow, my XOR gate output doesn't change at all, and the NIM-logic stays constant at -15 mA whether or not my input switch is closed (while the output of the logic gate is between -0.5 and -0.6 V). This behavior also occurs when a gate input is set to VCC (+5V).
Seeing as how this is not behaving correctly, I swapped out the IC with the DM7404N hex inverter IC. Logically, it should behave as if one of the XOR inputs is set to VCC, logic high. Swapping it out and putting a pull-down resistor at the input, the circuit behaves exactly as I hoped it would. The output of the inverter goes from 0.7 V to 3.4V depending on the input, and the NIM current correctly goes from -15 mA to 0. Seeing as how the circuit works with the inverter and not with the XOR gate, I was wondering what could be the reason why? I thought that perhaps the inverter circuit is more simple and allows for larger output current than the XOR gate, but I wonder if that is truly the case?
To be fair, there have been instances where using the XOR gate gives the correct intended result, but this doesn't seem to be consistent anymore. Whereas with the inverter replacing the XOR gate, it seems to work all the time.
EDIT: After reading the comments, I thought to try to use a different XOR gate of a different technology type, specifically the MC14507, the CD4030AY, and the SCC4070BE. I did some research and found that these gates are based on MOS technology which should allow for more current flow, and that seems to be the case. The NIM logic signal switches consistently, so is it safe to assume that all my problems are just using the LS XOR gate?