The 6JH6 is described as a semi remote cut off pentode (Variable μ) for use in television receivers within the IF strip. Thus it was designed to provide wideband amplification at 30 - 40 MHz.
The bright beam plate reveals that this is constructed as a beam tetrode. The two inner grids pass flat across the cathode.
The two part anode with strap across the grid ends. The beam plate is clearly seen as is the shape of the screen grid winding.
The thin glass tube envelope is 18 mm in diameter, and excluding the B7G base pins is 46 mm tall.
References: Data-sheet. Type 6JH6 was first introduced in 1955. See also1955 adverts.