21 RADIO TRANSMITTERS, AND COMPONENT PARTS THEREOF (INCLUDING POWER SUPPLIES, MODULATORS, RELAY RACKS, QUARTZ CRYSTALS, TRANSFORMERS, SPEECH EQUIPMENT COMPRISING AUDIO FREQUENCY AMPLIFIER CIRCUITS, MIXING AND CONTROL CIRCUITS, ELECTRICAL CONNECTIONS FOR MICROPHONES AND OTHER SIGNAL SOURCES ADAPTED TO BE USED THEREWITH); AND RADIO RECEIVERS, AND COMPONENT PARTS THEREOF