An 8-pin plastic base with center post. Mica insulator. T-shaped glass envelope. Printed on base: "Engineering Sample / A / 3 / Ken-Rad / Made in U.S.A."; on envelope: "12AH7 / GT". Paper label reads: "Laboratory sample / Type 12AH7GT Date 1-31-[19]41 / Ken-Rad Tube and Lamp Corporation / Incorporated / Owensboro Kentucky". Reference: https://www.radiomuseum.org/tubes/tube_12ah7gt.html.