ELECTRICAL METHODS 



621 



Power may also be obtained from a specially designed 500-cycle 75- 

 watt hand-cranked alternator, an interior view of which is shown in 

 Figure 389. Two handles are provided for cranking. These are con- 

 nected to a gear driving the alternator. The alternator turns over at a 

 speed of 4000 r.p.m., and the cranks rotate at a speed of approximately 100 



Fig. 388. — High frequency energizing system in 

 opei-ation: a, high frequency coil; b, folding coil sup- 

 port; c, tripod head allows rotation about vertical axis; 

 d, high frequency oscillator; e, battery compartment. 



r.p.m. Ball bearings which are provided throughout facilitate the cranking 

 required to generate the necessary power. Approximately 50 watts input 

 is required for operation of the high frequency apparatus. Direct current 

 for the field of the alternator is supplied from three No. 6 dry cells. The 

 entire apparatus is contained in a steel waterproof case. 



Figure 390 gives the wiring diagram for the oscillator when using 

 alternating current for supplying power. The output of the two tubes 

 shown is practically the same as would be obtained from one tube when 

 direct current is employed for plate supply. 



