The 12BH7A double triode is pin compatible with the ECC81,2,3 series from Mullard but has slightly different characteristics. Brimar originally gave an intended use as a TV frame valve for wide deflection angle tubes, but the construction is compatible with audio through to low VHF use.
Modern valves made by the Slovak company JJ Electronic are made especially for audio applications.
The anode face view. The construction is designed for an anode dissipation of 3.5 Watts and has a large anode and the control grid is wound on copper supports. The original 12BH7 was also had a 3.5 Watt anode dissipation whereas the ECC82 has a 2.5 Watt anode dissipation.
The ends of the anodes.
See alsoECC99 a specially developed 3.5 Watt dissipation double triode for driver applications.
The thin glass tube envelope is 21 mm in diameter and excluding the B9A base pins the length is 50 mm.