The L63 is an octal based amplifier triode. It is a low impedance device and although designed as a general purpose valve it is often used at audio frequencies.
The reverse has the Type designation of 6J5G and Admiralty Pattern W1528A clearly indicating that this was supplied to the UK Navy.
The dome with the fingers of the mica holding the electrodes firmly to the inside of the glass. The cathode is a round tube and the grid supports can be seen.
The classic envelope is 38 mm in diameter and, excluding the IO base pins, is 85 mm tall.
References: Data-sheet & 1040. Type L63 was first introduced in 1938. See also1938 adverts.
