[MrFixr55]

Given the 1960s vintage, it is likely that the cartridge is ceramic, likely more stable. The changer looks like a Voice of Music. Interesting that it can mix 7, 10 and 12, and change speeds? VoM changers had 2 sensors one came up to sense a record.
The other was triggered as the record dropped. If both sensors were activated, it was a 12" record. If only the sensor that came up to sense a record was triggered, it was a 10" record. If neither, it was a 7" record. I believe the average VoM could intermix 10 and 12"records. This must have had a different sensor, as with the 12" diameter platter, the unit does not have the 10" sensor. I believe that newer VMs with the 12" platter would have only the one sensor. If it was triggered, it was a 12" record, if not, it was a 10 or 7" record. It is likely that setting the speed to 45 rpm dictated the turntable to act as if the record was 7". So this must have had a sensor that measured the size of each record that dropped.

78s came in 10" and 12" size. There were also 7" 78s, mostly children's records. Almost all LPs were 33 1/3RPM and 12". There were "transcription disks" of radio shows that were 16" and would not fit on consumer record changers. So there must have been some real mechanical smarts to determine speed by record size.

All Genie (single play portable) record players, all VoM, Garrard, BSR and Collaro changers of the 1960s vintage in consumer level electronics used a "capstan" drive where a spring loaded rubber wheel, contacted both the motor armature and inner rim of the turntable. These wheels do dry out and the spring tires, causing stalling as the change mechanism operates. the change mechanism is driven by a gear at the center of the turntable. In addition, the grease used to lubricate the mechanism gets hard and becomes glue instead of lube. If the changer is a VoM, the wheel may be available. There is a website for VoM changers that offers advice and some parts.

I do hope that you find a home for it or get it working yourself. I would love to see a schematic or pix of the amp section.