Submarine Signal Company book page scan, showing the Fessenden Fathometer system:
Cover of the amplifier:
Inside:
(The tube panel also drops down. Behind it is the battery compartment.)
T. Woofenden Collection
Submarine Signal Company book page scan, showing the Fessenden Fathometer system:
Cover of the amplifier:
Inside:
(The tube panel also drops down. Behind it is the battery compartment.)
T. Woofenden Collection