Federal type 30 radio frequency transformer on base, "Federal Telephone & Telegraph Co. / Buffalo, N.Y. / U.S.A. / Type No. 30 / 275-600 meters". Commercial radio frequency coil covering 275-600 ...
A square black metal housing enclosing a transformer, two contacts on front and two on back. Stamped on back: “Type 271 / M.F. Transformer / G. Sec”; on front: “General Radio Co. / Cambridge, Mass. / ...
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