Long experience in the use of audio frequency buzzers to modulate the output of a tube set to produce damped wave trains has proven that this method is not entirely satisfactory, principally for the reasons that the operation of the buzzer is not constant, necessitating frequent adjustment, and that great care is required in adjusting the circuit to obtain 100 per cent. modulation.

   The Rotary Chopper, PX-1638, has been developed primarily to overcome the above objections. It may, however, be used in numerous circuits for this or other purposes where an interrupter is required. When used to secure I. C. W. telegraphy, the motor-driven interrupter, or rotary grid chopper, has the following inherent advantages over the other methods:

(a) Gives positive interruption, requiring no adjustments. The note obtained can be varied to any desired pitch by changing the driving motor speed.

(b) This system of securing damped wave trains does not require modulating tubes, the interrupter being used in series with the transmitting key.

(c) The system inherently gives 100 per cent. modulation, since oscillations can be completely started and stopped at audio frequencies.

(d) The output obtained from a given number of oscillators is in general greater than if some of the tubes are used as modulators.

The equipment includes the following parts:

(a) Interrupter Wheel, Model PX-1638.

(b) Two Bushings, so that the wheel may be mounted on motor shafts ¼ in., 5/16 in., or 3/8 in. diameter.

(c) Brush Holder and Brush.

The interrupter wheel is built with 34 conducting and 34 insulating segments, making 34 interruptions per revolution. The insulating segments are molded in a single piece.

Motor-Driven Chopper, PX-1638 . . . . . . . . . . . $7.25
    Dimensions: 4 in.x 134 in.
    Shipping Weight: 3 lbs.

Shaft Bushings, Model PX-1640, for 5/16 in. or

    PX-1641, ¼ in. Motor Shaft, . . . . . . . . . . . . . .   .20