The Mechanism - 78 RPM versus 45 RPM
I recently secured an original 'Service School MANUAL Number One'.
I can appreciate the 1948 notes scratched on the cover basically equating the 'SLBA1' to the circled 'SL1' + circled 'BA1'.
While the groundbreaking Select-O-Matic Mechanism remained, in theory, largely "unchanged" for decades, there were distinct differences. Ron Rich provides excellent detailed summaries in his "Seeburg Mechanism Guide" including the reasons behind why the M100A unique sequence of operations was sometimes resurrected for use in later models.
The 'SEQUENCE OF PLAYING' summaries at the bottom of this page identify the primary difference between the 78 RPM Mechanism and that of the 45 RPM model.
The overall section though remains focused on the SICM.
Seeburg Industrial Commercial Music.
Service School MANUAL Number One -- SICM
SELECT-O-MATIC LIBRARY, Type 200S3-L6 (78 RPM)
The Selectomatic Library, Type 200S3-L6, is designed for automatic, selective playing of any of the selections in a library of 100 records. It is designed for use with standard 78 r.p.m., lateral cut, 10" or 12" disc recordings and will play either side or both sides of the records.
There are two fundamental parts of the Library -- a magazine, and a carriage assembly. The magazine holds the library of records. The carriage assembly plays the desired program selections by progressively withdrawing the records, playing them, and restoring them to their original position in the Library magazine.
The records are in a vertical position ("on edge") at all times while in the Library -- in the magazine, during transfer to and from the playing position, and when playing.
MOTOR
All phases of operation of the carriage assembly -- scanning, transfer of the record to and from the flywheel, and playing of the record -- are accomplished with a single motor mounted on the carriage assembly.
The change in direction of scanning and playing of the left or right side of a record requires a change in direction of rotation of the motor.
SEQUENCE OF PLAYING ( 78 RPM )
The sequence of playing of records for a program will be established by their position in the Library, because the scanning operation of the carriage assembly is interrupted for playing a record only when the direction of scanning is from left to right.
If both sides of a record are to be played, the left side will play first, then, immediately after, the right side will play.
When the carriage assembly reaches the rightmost portion of the magazine (as viewed from the front), the carriage assembly / mechanism reverses direction and travels the entire length of the magazine, akin to an old classic typewriter, bypassing any selections, until it reaches the leftmost portion of the magazine where it reverses direction again, and begins scanning left to right seeking and playing any selections.
SEQUENCE OF PLAYING ( E A R L Y 45 RPM )
The carriage assembly changes direction of scanning only at the ends of the magazine, and the scanning operation is interrupted for playing only when the carriage is scanning toward the selected side of the record. Selections of the left sides of records will be played as the carriage progresses from the left side of the magazine --- right sides as the carriage scans from the right side. If both sides of a record are selected, one side will be played, the carriage will then progress to the end of the magazine and reverse direction, before playing the remaining side.