Sensibly equivalent¶ to:
The VT127 is an early television line output pentode valve and the VT stands for Valve Transmitting in the pre-CV RAF naming system. This example was made in USA for the RAF and also carries the Air Ministry Logo.
In line scan duty high surge voltages appear, this valve can withstand an anode surge of 3,000 Volts.
The box anode is supported on ceramic insulators. The two inner grids are supported on notched copper rods. The suppressor grid appears to be beam plates in this valve. The Pen46 has a wire wound third grid.
Some of the (earlier) Mazda 'Pen' series were true pentodes (eg. AC/Pen, AC2/Pen) while others (later) were definitely beam tetrodes (eg. AC4/Pen, AC5/Pen). It is quite possible that both varieties of Pen46 were made. Basically, in the early 1930s Mazda pentodes were the best in Europe, far surpassing M-OV's efforts in this direction. By the later 1930s, M-OV and RCA had co-operatively developed a family of beam tetrodes which were significantly better than the best Mazda pentodes. Mazda gradually climbed onto the beam tetrode bandwagon but, whereas M-OV proudly advertised their 'KTs', Mazda concealed the change to beam valves from all but the technical cognoscenti.
Given that only Mazda made valves on the Mazda Octal (MO) base and that this is made in the USA and has a UK Government code it was probably made during WWII.
The the crown and AM of the Air Ministry Logo.
The control grid has a radiating element added and copper support wires. The beam plates can be seen to be supported by tabs whereas the screen grid is wound on notched rods.
The components below the bottom mica. The insulated heater can be seen to pass four times through the rectangular cathode.
In this image the construction is easier to see.
The classic envelope is 50 mm in diameter and, excluding the MO base pins, is 118 mm tall.
References: Datasheet & private correspondence. Type VT127 was first introduced in 1940.
Absolute Maximum Operating Conditions¶
Updated April 04, 2015. shape:classic construction:pinch type:pentode age:1930.1940 base:mo heater:4.0v pins:8 pin:1.h pin:2.k pin:3.- pin:4.g2 pin:5.g1 pin:6.- pin:7.- pin:8.h pin:tc.a