The KT33C is described as a beam pentode, virtually another name for the beam tetrode. This is an audio device and the heater has a centre tap, suggesting that 26 Volts at 300 mA is another specification for the heater.
In single ended use the load impedance is given as 3,000 Ohms. For push pull the input voltage peak to peak would be 44 Volts, the load impedance would be 4,000 Ohms, and the ratings are given for Class AB1.
The Marconi label on this M-OV made valve.
Looking up from the base under the carbon film on the inner of the glass the anode can be seen above the lower mica. The construction is a rounded central section with side fins.
The classic envelope is 44 mm in diameter and, excluding the IO base pins, is 106 mm tall.
References: Data-sheet & 1043. Type KT33C was first introduced in 1939.