An Inexpensive Direct Current Amplifier

In an attempt to increase the stable sensitivity of the direct current amplifier designed by Voorhis, it developed that the commercial tube, type 2A6, is particularly suited to such work. A single 2A6 in a circuit similar to that of Sallu gave a sensitivity of 3xl0-3 amps/mm. with a galvanometer of sensitivity, 10-8 amps/mm. An arrangement with a portable microammeter and an a.c. power supply resulted in a useful portable high impedance galvanometer with a sensitivity of 10-11 amps/mm. The circuit is discussed and methods of balancing explained. It is shown that adjustments are not critical and the amplifier is sufficiently stable