The 6U8A is a triode pentode by designation but is constructed as a beam tetrode. The 6U8A differs from the 6U8 mainly in the fact that the heating time is tightly controlled.
The design purpose was in VHF radio and television between 80 MHz to 220 MHz. Bands II and III. The valve would be used as a mixer with the triode as local oscillator.
The 6U8A was used in many colour television chassis. The triode is medium μ and the pentode is a sharp cut-off type. The 6U8A can be used to replace 6GH8 or 6EA8.
This image is taken looking into the pentode section. The working anode parts are to the left and right and carbonised to radiate heat. The centre bright component is the beam forming plate. Dead centre can be seen the screen grid wound on a bright support. The inner control grid is wound on copper supports.
The anode in close-up. The sharply bent corners of the screen grid wire are clearly seen as are the copper supports for the control grid above the top mica.
The triode also has copper control grid supports.
The triode front elevation in the foreground.
A closer look at the centre electrodes of the pentode.
The thin glass tube envelope is 20 mm in diameter, and excluding the B9A base pins is 51 mm tall.