Note
QST, Jul 1954, p. 135.
QST, Dec 1954, p 112.
QST, Jul 1955, p. 100.
QST, Mar 1956, p. 133.
A reference in CQ, Feb 1964, p. 55 ("New Products") indicates the PR-1 was made by Singer Company, Metrics Division. Note that this reference occurs ten years after the PR-1 was first advertised. Is this a re-introduction? Or maybe an error.
References
Brief description. Electronics World, Oct 1965, p. 97.