There is a wealth of information out there.  Many of the home
changers we came to love were invented by J.P. Seeburg, Philco, RCA and
Capehart.

The changer everyone knows today, if you're over 40, is the central
spindle model.  The records were stacked on top and held in place by a
lip in spindle shaft.  Hitting the reject switch caused the tone arm to
lift and return back home, and the next record to fall to the turntable
and the tone arm to placed at the beginning of the next record.

Most late models were either 3- or 4-speed with a double needle.
A 3-mil needle for 78s and a 1-mil for micro grove 45, 33 and 16 rpm.
They also usually had a manual select switch for 12, 10 or 7 inch
records.  Enough said !

The two books I have are "Pin-point Record Changer Troubles in 5
Minutes" by the Coyne Publication Co., Copyright 1958. and "Automatic
Record Changers and Recorders" by John J Rider, Copyright 1941.  Hope
this helps.

Chris Kalstone