Kepco Series APH Power Supplies are high voltage, low current, precision-stabilized d-c sources of approximately twenty watts of d-c output power. Their important design features include: a) AUTOMATIC CROSSOVER BETWEEN VOLTAGE AND CURRENT STABILIZATION MODE OF OPERATION WITH VISUAL FRONT PANEL (LED) MODE INDICATORS. b) PRECISION, TEN-TURN FRONT PANEL OUTPUT VOLTAGE AND OUTPUT CURRENT CONTROLS. c) RECESSED FRONT PANEL OUTPUT METERS PERMIT THE SIMULTANEOUS MONITORING OF OUTPUT VOLTAGE AND OUTPUT CURRENT. d) FRONT AND REAR OUTPUT TERMINALS WITH REMOTE SENSING PROVISION, ALLOW PRECISION STABILIZATION AT A DISTANT LOAD. e) PROGRAMMING TERMINALS PERMIT ACCESS TO A BUILT-IN, INDEPENDENT PREAMPLIFIER, TO THE VOLTAGE CONTROL AND MAIN VOLTAGE AMPLIFIERS AND TO A SEPARATE CURRENT CONTROL AMPLIFIER. A MODE FLAG SIGNAL OUTPUT (TTL COMPATIBLE), AS WELL AS TWO D-C REFERENCE SOURCES (±6.2 volts at 1mA MAX.) REFERENCED TO COMMON (+ SENSE) ARE PROVIDED. 1-5 The APH Power Supply cart, in simplified form, be electrically represented by the fold-out diagram in Section ill of this manual (see FIG. 3-15 at the end of Section 111). A high voltage, low current d-c source is controlled by a series pass element (vacuum tube), which in turn is controlled by the driver circuit via the voltage channel or the current channel. The driver is connected to three contro1 amplifiers (Main Voltage, Internal Current Control, External Current Control) via the gating circuit, which permits only one amplifier to take control of the APH output.