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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 Raytheon name etched into the glass with VT127 and the old stores code of 10E/231.

made for the UK Air Ministry the envelope carries the AM and crown.

The box anode has a centre flange for extra heat radiating area.

The Ceramic insulators for the anode as high peak voltages are involved. The control grid has a heat sink at the top. The screen grid is wound of copper supports for good heat transfer.

The lower mica showing how the assembled valves was spot welded to the wires fixed into the pinch.

The classic envelope is 51 mm in diameter and, excluding the MO base pins, is 109 mm tall.

References: Data-sheet & private correspondence. Type VT127 was first introduced in 1940. See also 1940 adverts.

Pin Connections

Absolute Maximum Operating Conditions^¶

Thanks to Frank Philipse for supplying the above PDF datasheet.