The ECC83 high impedance amplifier triode was designed specifically for audio use and has a high amplification factor of 100. Mullard describe the ECC83 as a high μ double triode, having separate cathodes, primarily intended for use as a resistance-coupled amplifier or phase inverter.
Thorn took responsibility for the Thorn-AEI valve business after 1961.
The twin triodes.
The stitched anodes. Note that double micas are used in the assembly. This would confer vibration resistance and thus be used in professional and military equipment.
The thin glass tube envelope is 20 mm in diameter and, excluding the B9A base pins, is 49 mm tall.
References: Data-sheet, 3002 & 1040. Type ECC83 was first introduced in 1954. See also1954 adverts.