This paper describes in detail the equipment and circuit used in the production of the single sideband for trans-Atlantic radio telephony in the experiments at Rocky Point. The set consists of two oscillators, two sets of modulators, two filters, and a three-stage amplifier. The oscillators and modulators operate at power levels similar to those in high-frequency communication on land wires. The three-stage amplifier amplifies the sideband produced by these modulators to about a 500-W level for delivery to the water-cooled tube amplifiers. The first oscillator operates at about 33700 cycles, The modulator is balanced to eliminate the carrier; and the first filter selects the lower sideband In these trans-Atlantic experiments the second oscillator operated at 89200 cycles, but might operate anywhere between 74000 and 102000 cycles. The second modulator, which is also balanced, is supplied with a carrier by the second oscillator and with modulating currents by the first modulator and first filter. The second filter is built to transmit between 41000 and 71000 cycles, so that by varying the second oscillator the resulting sideband, which is the lower sideband produced in the second modulating process, may be placed anywhere between these two figures. Transmission curves for the filters are given as well as some amplitude-frequency performance curves of the set.