Show obviates necessity of excessive B battery questions are frequently asked regarding the use of tubes with a high amplification constant these tubes are primarily designed for use in resistance si and impedance amplifiers we ve a quote a few lines from one of keith hanneys Hen Hea tube articles in the radio broadcast magazine he writes as follows A low mu tube will not load up a power amplifier unless coupled to it by means of a transformer for example the average amplifier to deliver 00 watts power requires at least 9 volts variation on its grid A tube w with ith a mu of 8 coupled by means of f resistance impedance to the amplifier fir cannot produce a variation of voltage greater than 8 volts and probably not over 0 so that the amp amplifier amplified lifie r w will I 1 n not at deliver its rated quota of 0 power on the other hand a tube with a mu of 20 or a tube with a mu of 5 coupled by means of a 21 transformer can easily produce the desired change chance in input voltage high mu tubes can be used as detectors and hence are useful in vacuum tube voltmeters their use in resistance and impedance amplifiers fiers make the latter practical without increasing the B V battery voltage beyond reason it must be said here that the mu of such tubes to Is not the only important constant the plate impedance must be considered and like all other tubes the usefulness of bagh mu inu tubes increases as their impedance decreases in this question it must be remarked that tubes of 1020 1026 differ from those of 1025 1925 in the fact that their plate impedance la Is less this to Is duo due to the use of better filament wre which has a higher electron efficiency this low impedance while it makes good amplifiers causes trouble when the tubes are used in sets that have been neutralized for high impedance tubes it ii Is well known that less inductance duc tance Is required in the plate circuit of low impedance tubes to make them oscillate than Is the case with high impedance tubes on the other hand band once these newer dewer tubes are neutralized the voltage amplification and power output are increased |