The ECC83 copy from Zaerix was made in the German Democratic Rebublic, what we used to call East Germany, and imported into the UK.
The Mullard ECC83 is high impedance amplifier triode was designed specifically for audio use and has a high amplification factor of 100.
The thin glass tube envelope is 21 mm in diameter, and excluding the B9A base pins is 48 mm tall.
References: Datasheet, 3002 & 1040. Type ECC83 was first introduced in 1954.