45 RPM Mechanism - Video 1

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Note: In both videos, should the tonearm already reside on the appropriate side of the record, no flop takes place.

So, inherent to this design is: the relative "right" side of the records, as viewed from the front of the jukebox, are played as the mechanism scans right to left.  Similarly, as the mechanism scans left to right, all "left" sides of records are played.

Having had this brief overview, let's now look at the Seeburg 78 RPM Library Unit Mechanism.  For what is covered here, the M100A 78 RPM Mechanism also applies.

However, in opening, it is important to note two basic points between the 45 RPM model and the 78 RPM model:

In common:

-- Both the 45 RPM unit and 78 RPM unit required the tonearm to "flop" to the appropriate side of the record when necessary.

Not in common:

-- Whereas the 45 RPM unit selected records when traveling in EITHER direction (as seen in Videos 1 and 2), the 78 RPM unit selected records ONLY when traveling in ONE direction; NOT the other.  Once the mechanism reached the end of the magazine, the motor would reverse direction and the mechanism would travel the ENTIRE length of the magazine (without selecting a record), reverse direction again, and begin selecting and playing records.

In this 1st Video of the 78 RPM Library Unit, the "least" complicated Sequence of Operations takes place.  As the Mechanism scans Left to Right as seen from the front of the unit, the flywheel spins counterclockwise.  Selected for play was the Left side of the record.  You may have noticed that the tonearm remained stationary prior to the record being raised to the flywheel.  This is because the prior record that had been played happened to also be the left side of the record.  Had, instead, the Right side of the record been played last, the tonearm would have flopped ahead of the record being raised to the flywheel (as seen in the 2nd 45 RPM video).

First, The motor (and flywheel) must switch direction and second, the tonearm must flop to the opposite side of the record.  Replay the video focusing only on the flywheel.  Note the switch in direction.  Replay the video again and this time focus on the base of the tonearm.  See how it toggles to the near side of the record. 

 The Seeburg M100A Jukebox Mechanism evolved from the Seeburg 78 RPM Library Unit.  As you're standing in front of the Library Unit, the mechanism scans Left to Right, seeking selections to play.  The mechanism itself is hidden from view.  Instead, the front of the unit features the 'magazine' bins; 100 vertical slots where records may be easily inserted, removed, and desired side(s) selected or skipped entirely, with the flip of a lever.

To over-simplify for this summary, the M100A Jukebox merely spun this entire mechanism around, so as to place in full view this new and exciting 'Select o matic' mechanism.  In 1948, Jukebox mechanisms were rarely in view.  Additionally, most jukeboxes were playing only 12 or 24 selections.  Seeburg 'revolutionized' the industry (embarking on the 'Silver Age' of Jukeboxes) with this fascinating gadget that played 100 selections!Seeburg's 'speed-to-market' even ignored the logical direction of the M100A mechanism which would be Left to Right.  Instead, the unit scans Right to Left seeking selections to play.

For both the Library Unit and the M100A Jukebox, selections only occur in one direction.  The 'reverse' direction of the mechanism merely acts as a return, traveling the entire length of the magazine, bypassing all selections.

So, while the demonstration video below is that of the Library Unit mechanism (from behind), it serves too as the M100A Jukebox mechanism (from the front).  Understand the demonstration is purely from a flywheel directional, tonearm behavior, one-side-only, both-sides, other-side-only point of view.  As eluded, the M100A mechanism had adopted many design variances for switches and relays by the time of its introduction.