[Randy Bassham]

I believe the sizes are 1 mil for LP/45's and 3 mil for 78's. The early Zenith "Radionic" pickups for the Cobra turntables did not generate a voltage, the needle was connected to a small round disk that was put directly in front of a coil of wire that was in the circuit of an oscillator. The movement of the disk changed the "Q" of the coil and varied the output amplitude of the oscillator, which was detected by the second half of the "Radionic" tube, in my 12H094 I believe it's a 7H7 dual triode. The output of the detector is fed into the amplifier of the radio. It's quite a circuit and as Chad says it works quite well for 78's. The 3 mil "Red" cartridges are getting hard to find and commonly what you will find are the 2 mil "Red/Green's" that were sold as all speed but I don't think they sound as good. The "Green" cartridges were 1 mil for Microgroove records LP's and 45's.

There was a later version of the Radionic cartridge that was used in monaural sets but when Stereo came in the design was apparently not suited to Stereo, and Zenith continued to use the tone arm with the little eyes but they had conventional crystal/ceramic pickups usually with Voice of Music supplied turntables.