The post about the Stax and Weathers pickups jogged my memory.
When my sister was born in 1948 my father splurged with the tax deduction and bought a Zenith table "hifi" with am, fm, 78 rpm and the then new 33 rpm.
The auto changer had 2 tone arms, one in maroon for auto changer play of 78s and a second green arm for manual play of 33s. The pickup was a tiny thing about 1/4 wide by 1/2 long by maybe 3/32 thick and very light. It plugged into electrical contacts in the arm. Since the stylus 3 mil for 78, 1 mil for 33 was integral to the pickup we had old worn ones sitting around. Out of curiousity we split one open. Very little to see, the stylus attached to - as I remember - a tiny circular piece of metal adjacent to a tiny coil. I just Googled "Zenith Cobra arm" and found this:
"Radionic" phono circuit
The schematic for this set shows a 6J5 tube as "phono oscillator". Apparently the Zenith Radionic Cobra cartridges vary the "Q" of a tiny inductor to modulate a 2.5 MHz oscillator. This is fed directly to the receiver which detects and amplifies the signal. Unusual to say the least.
So the circular metal plate and coil formed the inductor. It would seem that the potential was there for a low mass, light tracking device - but it wasn't so!
Didn't Weathers also produce turntables? Perhaps also satellite speakers disguised as books and a small common woofer? There were such wonders in the Allied Radio and Lafayette catalogs, back in the day!