The ESgar Model 121B Power Source provides AC power at precise frequencies for testing, motor operation, and frequency conversion. The basic power amplifier consists of two DC supplies and a direct-coupled ampiifier with a tapped output transformer. The output transformer provides nominal output voltages of 115 and 220 VAC that are adjustable between 0-125 and 0*250 VAC. The total available power is 120 volt-amperes at full rated output voltage. Power at less than full-rated output voltage is derated as illustrated in Figure 1-1. Shown in Figure 1-2 is a curve of typical harmonic distortion. Input power is 50-60 Hz. The power transformer may be wired for 230V at 50-60 Hz. 1-5. Output power frequency is established by a plug-in oscillator. Output frequency range is 45 to 10 KHz. A variety of plug-in oscillators is available with frequency accuracies up to .0001%. 1-6. The Elgar Power Source facilitates equipment tests to meet military specification operating requirements over the frequency range of 47 to 63 Hz or 47 to 425 Hz. The basic power source output is single-phase. Multiphase power can be obtained however, by stacking two or three power sources, all driven by the same multi-phase plug-in oscillator. 1-7. GENERAL DESCRIPTION 1-8. The Elgar Model 1 21B Power Source is contained in a rack mount enclosure. A meter for output voltage monitoring, a power-on Indicator, a voltage amplitude control and a power circuit breaker that applies line power to the unit are located on the front panel. Cooling air is drawn through a front-panel grill and exhausted at the rear of the enclosure. 1-9. The enclosure contains two heat-sink assemblies, which comprise a two-section power amplifier. Control circuitry is mounted on a circuit board with test points and adjustment controls available on the top side of the board. Output power is available at the rear panel terminal block and across the red and white binding posts located on the front panel.