The 6336A is a purpose designed series pass valve for use in stabilised voltage supplies and similar DC control applications. It is mechanically rugged and it is claimed to be able to replace two or three type 6080A double triodes. The PDF data sheet dates its introduction to 1958.
The zirconium coated graphite anode is not only able to withstand high temperatures but is also a very effective getter.
The type designation etched into the dome.
The gold plated molybdenum wire grids are supported on sturdy copper supports for better heat dissipation.
The top of the valve showing the getter holders.
The octal base.
The classic envelope is 51 mm in diameter, and excluding the IO base pins is 95 mm tall.
Reference: Data-sheet. Type 6336A was first introduced in 1958.