Low voltage AC power for thermocouple tube?
I am trying to make a readout for a DV-6M thermocouple gauge tube to measure vacuum. The tube requires 380mV (0.38v) AC across its filament to operate, and anything more could burn the filament. (I was reading up on this tube, and found the filament has a resistance of 18ohms but if you tried to measure it with a multimeter you could burn the filament). I have modified a 555 tone generator circuit, to accomplish this, and have measured the output to be 380mV AC with my fluke multimeter, and 0mv DC. When I put an LED across the output leads however, the LED is able to light which should take around 3v, which makes me wary of trying to connect it to my tube. what is happening, and is it really producing 380mV AC or is something else going on?