MARCHI

Philco began in the battery business, not in vacuum tubes. Philadelphia Storage Battery Company, founded in 1892, supplied the power needed by early radios: batteries for filaments, anodes and bias. When mains-powered receivers reduced the importance of that market, the company moved into making radio sets. From 1927 Philco became the name of a major American receiver maker; tubes were central to its products and service network.

Philco-branded tubes were sold to equip and repair those receivers. The name printed on a tube does not, however, prove that Philco physically manufactured it: in the early years the brand also used outside producers. An important change came in 1940, when Philco acquired a controlling interest in National Union Radio Corporation, an established tube maker. The relationship brought the receiver brand and tube production closer together without automatically erasing National Union's separate identity.

Philco is thus a case where tube history is intertwined with that of the receiver, replacement sales and industrial organization. Sales catalogues explicitly offered Philco tubes to owners of its sets; advertising presented the brand as a guarantee of compatibility and continuing service. To determine the actual origin of an example, its carton and Philco marking are starting points to be read alongside its type, date and any factory codes.