A metal pin-and-blade base with top contact, G-shaped envelope with neck. Stamped on base: “Federal”. Donor’s card reads: “Half-wave mercury vapor rectifier made by the Federal Telegraph Company, ...
A 4-pin plastic base, top contact, S-shaped envelope. Donor’s card reads: “Half wave mercury vapor rectifier made by the General Electric Company for the Radio Corporation of America in January 1929.
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