Tube mics are shaped like a tube, or cylindar, whereas an FET condenser has a pointy end, like a ferrit. They contract the name to FET 'cause ferrit is bad marketing and FET sounds technical.
Gaaaaa!!!!! NO!!!!! I can't go through with this!
A tube mic uses a vacuum tube as the head amplifier! An FET uses a field effect transistor for the amp. Both can then either use a transformer to get the output to low impedance audio level, or can also use another FET to do the job.