General Electric describe this as a sheet-beam tube. Elsewhere this type of valve is called a beam deflection tube.
A stream of electrons is modulated and accelerated in the usual way, but there are two anodes and a pair of deflection electrodes, like the plates in a cathode-ray tube. The beam can thus be switched between the anodes totally or in part. This function makes balanced modulators, and synchronous detectors possible.
GE give the use for the 6JH8 as a synchronous detector in a colour television receiver.
The GE logo.
A maker's code. The internal structure is not visible, only the copper grid supports.
The thin glass tube envelope is 21 mm in diameter and, excluding the B9A base pins, is 59 mm tall.
Reference: Data-sheet. Type 6JH8 was first introduced in 1961.