The 19BG6G is described in the data-sheet as basically a 6L6G redesigned for use as a television line output valve. It is fitted with a 300mA heater for series heater chain use. The main change in the valve is better insulation to cope with the high peak anode voltages.
The Type designation and the working face of the anode.
A side view of the anode.
The control grid is wound on copper supports. The beam plates are blackened. The notches on the two sets of grid supports look to be of equal spacing and aligned vertically. The grid alignment reduces screen current.
The classic envelope is 50 mm in diameter, and excluding the IO base pins is 124 mm tall.
Reference: Datasheet. Type 19BG6G was first introduced in 1949.