The VT51 battery audio output pentode was capable of 1.1 Watts at 7% distortion.
This specimen is characteristically Cossor shaped and will be a Cossor Type 220PT rather than a Mazda Type Pen220A. Originally designed as audio output pentodes these economical valves found numerous uses in portable battery-powered military transmitters.
The bright anode within the typical Cossor envelope of the period.
The top mica showing the filament tension springs, oxide coated filament wires and the two inner grids. The suppressor grid is missing but at either side are curved plates making this a beam tetrode construction. VT51 has the original three grid structure as do our other examples of this Type.
A closer view where the beam plates are clearly visible.
The classic envelope is 44 mm in diameter and, excluding the B5 base pins, is 95 mm tall.
References: Data-sheet & 1043. Type VT51 was first introduced in 1933. See also1933 adverts.
