The 6L1 is a low impedance double triode. The 20L1 has identical operating characteristics but is designed for use with 12.6 Volts at 200 mA on the heater thus making it suitable for vehicle use.
The twin triode sections. The equi-spaced eight base pins required an external location device, on this exhibit the first B8A base type is shown with a metal skirt, spigot and locating pip. Ultimately the wide diameter base was moulded into the glass together with the locating pip. The spigot disappeared quickly followed by the B8A base - replaced by B7G and B9A.
The triode with side flanges for cooling.
The thin glass tube envelope is 20 mm in diameter and, excluding the B8A base pins, is 52 mm tall.
References: Data-sheet & 1040. Type 6L1 was first introduced in 1951. See also1951 adverts.
