NOS in original military boxes marked "inspected 12/1955". Lower wattage than 6L6GCs (19 watts). Perfect anywhere 5881s, 6L6Gs or EL37s are normally used. Plate voltage upper limit is spec'd at 450V in class AB1 (most guitar amps and many audiophile amps) circuits. Great in tweed Bassman and other tweed or tweed style 5881 or 6L6G amps.