The CV391 was designed for transmitter use in the HF and low VHF parts of the spectrum. The design was an 807 in an all glass format. However, the specification quotes the prototype as the LS650.
In addition to RF power, the valves were designated for service as audio power amplifiers. Here the valve was to operate in class AB1 and a pair would deliver 15 Watts at 3% total distortion.
The specification gives the base as B8G but Loctal or B8B is the usual name.
The STC logo. The box anode face view.
The cooling fins are placed in the centre of the working faces and the support struts are at their outer edges.
The wide glass tube envelope is 28 mm in diameter and, excluding the B8B base pins, is 75 mm tall.
References: 1040 & data-sheet Type CV391 was first introduced in 1957. See also1957 adverts.