Note
Radio, Jan 1940, p. 138.
Radio’s Master, 9th edition (1942), p. H-106.
QST, Jun 1947, p. 143.
Optional CPS-121 extra matching speaker.
CPO-120 for headphones only, except with the optional CPS-121 extra matching speaker.
CPO-124 has a built-in speaker.
Brief review: Radio, Jan 1940, p. 138.