Clocks with the Telechron Type F motor were introduced ca. 1932. The field coil unit is similar to that for the type B but slightly more compact. The rotor unit is smaller than a type B rotor because one reduction gear was eliminated, increasing the output speed from 1 revolution per minute to 3.6 revolutions per minute. Type F rotors have a two piece housing, with the main body being a die cast piece. Type F rotors for alarm clocks have a long shaft on the output pinion, and those for time only clocks have a short shaft.
Clocks with the Type H motor were introduced in 1937. The Type H has the same internal gearing as the Type F, but has a stamped housing instead of the bulky cast housing of the Type F. Some early H rotors have a long shaft output pinion, but most have a short shaft. The H motor became standard for domestic clocks, and was used for many years.
Dave Friedlund, who rebuilds and sells Telechron rotors, has collected rotor data and interpreted their date codes. His sample data (combined with mine) show the following rotor production dates:
The meaning of the designations after the motor type (such as the H3 HNK or H3-HP) are unknown to me.
The most recently made H rotors (from the 1970's and on) have aluminum housings.
I have two other early H rotors with mounting feet. They are labeled:
H-3 TOP M1313
3.6 RPM 60-C 99_
99 is the date code for September 1939.
60-3 6 710
710 is the date code for October 1937.
There is no company name on either rotor
I have two type F rotors with standard length output pinion. They are both labeled as follows:
60-3 6 512
512 is the date code for December 1935.
The letter in a clock's model number indicates the type of motor it was originally designed for. For example, a 7H98 uses an H motor. Some clocks with F in the model number contain an H motor. A 7F59 contained the F1 rotor shown at the top of this page. Models 2F02, F 327*, 7F71 and 8F03 that I examined had a standard silver color H rotor. An alarm clock made for a type F motor would have been designed for the long shaft pinion. But starting in 1937 the same model would have been made to take the short shaft type H motor.
*Note on the F 327. This clock is listed as model 327 in Jim Linz's Telechron clock book. Here is a theory: Since model 327 was introduced in 1931, but the F motor was not introduced until 1932, the first ones had "B" motors. When the clock was redesigned to use the "F" motor, the F was added before the model number to identify this change.
Time only clocks made for a type F motor can have a regular type H motor put in. But alarm clocks made for a type F rotor were made for the long shaft output pinion, and needed the special long shaft H rotor when the original F rotor went bad.
Thanks to Jay Kennan for clarifying the dates of the F and H motors, and for explaining that the long shaft F rotors were for alarm clocks. Visit his Pappy's Telechron Clock Page for more history, and beautiful photos of hundreds of Telechron clocks.