The 30L1 is a double triode developed to meet the needs of VHF band III television transmission in the 1950s.
The 30L1 type of double triode was specifically designed for cascode operation. The normal configuration was for triode one to be operated as a grounded cathode stage directly coupled to triode two connected as a grounded grid stage.
The triode sections are mounted low in the envelope to minimise lead inductance.
The lettering shows a made in England valve.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 46 mm tall.
References: Datasheet & 1040 Type 30L1 was first introduced in 1954.