Above is the model of amplifier Tanner used in his Electro-Theremin. The Heathkit Model EA-2 12 Watt Amplifier was introduced Dec. 1, 1957, at a cost of $25.95 for the kit.

As can be seen in the picture of Paul Tanner playing the Electro-Theremin, he "road" the volume knob to control dynamics of the instrument. (see below)