Valve Preamplifier 2

EE 26 April 1987 VALVE PREAMPLIFIER 2 The main task of the boards de- scribed in this final instalment of the article is to enable the preamplifier to operate at the top of its potential. To ac- complish this, one board holds a relatively extensive power supply, the other a combination of logic circuits for driving the various relays in the preampli- fier. The power supply The present design is no ex- ception to the rule that high- quality AF circuits, whether preamplifiers or power ampli- fiers, invariably call for the use of no-compromise supplies that are based on the use of con- servatively rated components of the best quality available. The proposed supply is, therefore, a relatively complex circuit, set up to deliver three voltages to the preamplifier board, and two to the relay con- trol circuitry. The high-voltage (HV) rails for the preamplifier are stabilized with a series regulator to ensure optimum operation of the cascaded triodes, and also to effectively keep low-freq...