On the Detecting Efficiency of the Thermionic Detector

There is described a method of determining the detecting efficiency of vacuum tubes by feeding them with radio frequency current modulated at audio frequency. The theory of the method is given. In connection with such measurement, the use of a receiver shunt calibrated in terms of miles of "standard number 19 gauge cable" is advocated. For producing the radio frequency current for such measurement, a tube oscillator was employed. The audio frequency modulation was obtained either by a second tube or by a microphone howler. The apparatus is described in detail, and illustrated. Experimental data are given. A method for comparing the detecting efficiencies of a standard tube and of a tube under test is also described, and the apparatus is shown. In an Appendix, a simple method of measuring tube amplification is described.