I seem to recall that the auto-slide feature, at least for the general
public, arrived c. 1960. I remember the big too-doo about the Kodak
multi-slide exhibit at Grand Cenral just before the 1963-4 World's Fair.
When I worked there, I recall assembling shows for clients and adding the
triggering beep which had to be at a certain frequencey. It went onto the
"B" channel of a 2 track stereo tape.
I think many transcription houses had switched to 12" discs, especially for
the classroom market, as that's what I remember being the size player for
the film- record player machines of that era.
If anyone really cares, a look through the audio and educational audio
supply books of the period will have an answer.
From: Association for Recorded Sound Discussion List
[mailto:[log in to unmask]] On Behalf Of Art Shifrin
Sent: Thursday, August 02, 2012 7:52 AM
To: [log in to unmask]
Subject: [ARSCLIST] voca-film technology
Does anyone on this list know if the disks' tones were simply cues for the
operator to advance the slides, and or, if a frequency-tuned circuit
triggered the next slide?