Note
QST, Nov 1952, p. 91. (first ad)
QST, Dec 1964, p. 182. (now selling the movement separately)
QST, Apr 1974, p. 129. (close-out special - $12.00)
Pennwood was one of there very first (if not the first) companies to offer a mechanical digital clock. The company's name quickly became Pennwood Numechron, and later the name "Tymeter Electronics" was added to the moniker. Today, the clocks are commonly referred to as Numechrons or Tymeters.
The company's first models appeared about 1934, as seen, for example, in a 1934 catalog from the N. Shure Company. These were made with real walnut, as opposed to Bakelite used in most later types.
The model 100 clock (arguably the most popular model with amateur radio operators) dates from about 1938, and a 12-hour version can be found in Wholesale Radio Service Company's 1938 Lafayette catalog, where it is referred to as the "Chieftain," rather than the model 100. The 100 also appears in the 1956 John Plain company (Chicago) catalog where it is listed at the "Jefferson" model.
The clock mechanism uses a set of rotating wheels that periodically interlock to advance the time shown, and which are driven by a small electric motor. This scheme proved incredibly durable, with many examples from as early as the 1940s still running today.
Pennwood began advertising to the amateur radio market late in 1952--which may have coincided with the introduction of the 24-hour version of the clock-- and continued with not-quite-monthly ads until 1974, when the company was sold.
In addition to the 24-hour model 100, a clock with a ten minute call-identifier reminder (available in both 12- and 24-hour versions, models 112 and 124 respectively) appeared in 1959. A call-identifer reminder ten minute timer version with no clock (model 210) appeared around the same time.
Over the years Pennwood made versions of its mechanical digital clocks in dozens of styles, including versions that looked like miniature television sets. None had digits that were illuminated, but several models had switchable internal lamps (typically C7 "Christmas" bulbs) that let them function as night lights. Numerous small variations (notably the font type and color used for the numerals) occurred as the years ticked by.
Beginning in 1964, Pennwood also began offering just the clock mechanism and readout assembly, which found its way into countless amateur radio products including Heath's SB-630, Drake’s C-4, and Hallicrafters’ R-51, to name only three, as well as in the clocks of other manufactures including General Electric and Seth Thomas.
The model 100 can be seen in numerous shack photos appearing in popular hobby magazines.
Based on the longevity and popularity of the clocks, and by the number found on eBay and elsewhere, it is likely that many tens of thousands were sold. The clocks are not rare--though units in perfect condition are a bit more so--and can readily be found and purchased online. Be sure to ask if the motor runs quietly. Be sure to do separate searches for Numechron, Tymeter, and Pennwood, as many sellers use only one of those terms in their descriptions.
Common clock types include:
#100; 12 or 24 hour: basic clock
#112: 12 hour with call ID timer
#124: 24 hour with call ID timer
#210: ten minute call ID timer
#700 TV shaped clock
#765 TV shaped clock
References
Brief description (710-AG). Popular Electronics, Oct 1955, p. 72.
