The 6/30L2 is a general purpose double triode with a screen between the sections. Their main applications are found in television receivers. This Mullard implementation also has their own designation of ECC804 on the glass. The logo is the older style whereas ECC804 has the later logo.
One triode seen full face.
The two triodes with central electrostatic screen. The grids are wound on copper support rods.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 48 mm tall.
References: Datasheet & 1040 Type 6/30L2 was first introduced in 1958.