[wise65vw]

Okay, so I did some digging and discovered that the early d-10a changers, like the one in my 46-1203, DID use a crystal cartridge. However, the later units, like those in the 46-1209, used a magnetic cartridge. I looked under my tone arm, and sure enough, it had the screw hole placement for a crystal pickup (an Astatic L-70 or similar). It definitely explains why there's a slot in the tip of the tone arm.