Bell and Howell are known for their film projection equipment and this explains the brand 'Filmo' on the envelope. The valve is an own brand but not made by them.
The data sheet says the 6C6 design is very close to the 6J7G with the exception of the inter electrode capacitances. The 6C6 is a general purpose amplifier valve but the close similarities with the 6J7 indicate a good linear characteristic and good suitability for early stage audio amplification such as the output of a photocell reading the soundtrack on film.
The valve is a true pentode as can be seen from the three wire grids.
Turned through 90 degrees the relative diameters and pitches of the grids are clearly revealed.
The classic envelope is 38 mm in diameter, and excluding the UX6 base pins is 104 mm tall.
References: Data-sheet, 1040 & 1043. Type 6C6 was first introduced in 1936. See also1936 adverts.