> 75R to 300R Antenna adapter floating around????
> impedance for the antenna though
Don't make no difference. It's a Hallicrafters... it will pick-up Timbuctu. And his VCR or Digi-TV box's Ch3 output is very strong. Impedance mis-match is not going to matter. Cable don't matter. Alligator clips will work. Until last year, a foot of wet pasta would pick-up local TV.
Altho for other reasons, the input "must" be 50, 75, or 300. Coax is naturally 50 ohms. We can stretch it to 75 or 90 ohms. Twisted pair is naturally 100 ohms. Twin-lead stretches that to 300. Big spaced-pair can go 600. But rational design and cost keep us in the middle of this range.
Oh, 50 feet of line badly mismatched will add a ghost. Rather, a fringe on the right of each edge.
The one "gotcha": depending on year, he might have to hit button 2 to get what we call Channel 3. OTOH, "5" or "6" plus a big twiddle on button 14 might still pull in FM radio. Loud and distorted.
He's obviously joking us.
The other obvious use is an oscilloscope. It's electrostatic deflection. You need about 100V of drive signal, and the deflection voltage must be centered on one of the anode voltages. You can do it with a couple 300V transistors. The headache is building a semi-sync sweep. Or use a couple 6KCT:16 OTs backward from a stereo amp to make patterns.