A valve ammeter for the measurement of small alternating currents of radio frequency
H.E.M. Barlow · The journal of the Institution of Electrical Engineers · 1935
The paper describes an alternating-current milliammeter having four ranges, namely 5, 10, 20, and 30 milliamps, and suitable for measurements at any frequency from 25 to 5 × 106 cycles per sec. The instrument depends for its action on the use of a 2-electrode thermionic valve operating under saturation conditions in conjunction with a moving-coil galvanometer.