The Pen383 is a beam tetrode audio output valve on a Mazda Octal base that was designed for receivers operating without an isolating mains transformer. The design was released in 1938 with other valves to build superhet receivers. The Pen383 could produce just under three Watts of audio.
Through the internal coating can be seen the outline of the anode with holes at either end. The shapes under the lower mica suggest beam tetrode construction.
The identification is located on the top of the valve. The control grid has heat radiating fins at the top. The bright rod across the top is the connection to the rectangular cathode tube. The beam plates also connect to this cross bar.
The classic envelope is 54 mm in diameter, and excluding the MO base pins is 101 mm tall.
References: Data-sheet & 1043 Type Pen383 was first introduced in 1938. See also1938 adverts.
