KLH Receiver Design
Based on my research, there were three "generations" of design for KLH receivers from 1965 thru 1980:
1st Generation: the 'Henry Kloss' era:
The Model Twenty Seven was the only receiver of this era.
It's twin vernier tuning dials are a common theme of Henry Kloss designs. These units were manufactured in the US in the late 1960s.
2nd Generation: the "Singer" era:
The Model Fifty One was the only receiver of this era.
It's design is unique to this model. Linear Tuning Dial, metal and wood case. These units were manufactured in Japan in the early 1970s.
3rd Generation: the "Kyocera" era:
Multiple models ranging including 50, 52, 52A (Quad), 54, 55, 57, as well as the 71 and 72. These units had very conventional (bland) styling for the era: Black-out, linear tuning dial, silver face, rotary controls, and push button switches. These units were manufactured by Kyocera in Japan in the mid to late 1970s.