Dating the "70-L-7" tubes (Smithsonian NMAH; Valve Museum)

Investigator (STEP I), run 2026-10-08. Saved page text (evidence trail, not for publication) is in research/pages/. Findings are leads, not verdicts.

Searched

• Google: 70L7-GT tube introduced year rectifier beam power
• Opened: https://americanhistory.si.edu/collections/object/nmah_702597 (Chrome); fetched https://www.r-type.org/exhib/aaa1317.htm

Found

• Smithsonian NMAH, EM.313977: "Ken-Rad type 70L7GT halfwave rectifier, beam power tetrode", stamped "Engineering Sample / Ken-Rad", Related Dates "Ca 1939 (Date Made)".
• The Valve Museum: "The 70L7GT is an American valve designed for equipment without an isolating mains transformer ... Type 70L7GT was first introduced in 1947."
• Datasheets (snippets): a combined half-wave rectifier and beam power output tube "for service in AC-DC receivers".

Bearing on the claims

• Claim 2 (the Savo car): the summary says "Three of these tubes were model 70-L-7". Both dates found (about 1939 and 1947) are after 1931, and the two sources disagree with each other. Readings: a 36-year memory substituted a later, familiar tube type; the car was refitted later; or the episode is not of 1931. This is a lead for the reviewers, not a finding. An RCA or Ken-Rad tube release list would settle the introduction date.