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CHAPTER 14
VACUUM-TUBE OSCIILATORS
14-1. Oscilla.tor-circuit Arrangements . . Since th e power required by
the input of an amplifier tube is necessarily less than the am lified output, -"'.J./'it is ossible to rna e an amplifier su ly its own Iliut. When this is
done the result is an oscillator.
The typical oscillator is a tuned amplifier so arranged as to provide an
excitin between the grid and cathode of the tube that is approxi-mately 80° u f h 8e ·ith respect to the alternating voltage developed
(17' HtI,RTLE.'t (ol COLPITTS (c ) tUNED GRID tdl T\)NEfl PLATE
.Lg
Cg
Cgp Lp Cp
rl l ACTUAL CIRCUIT (f ) EQutVALENi CIRCUITS
TUNEO· GRIO - TUNEO PLATE
FIG. 14-1. Schematic circuits of common t.ypes of power oscillators.. To simplify thecircuit diagrams the methods of introducing the plate-supply voltage and of develop-
the grid bins are not shown, I
bejl.w€,en plate and cathode. This phase relation counteracts the phase..,'.er·sal produced by the amplifying operation, and 80 enables the exciting
VI),IT,".1YA to have the polarity required to generate the amplifier output.Sche:ms,tic diagrams of commonly used oscillator circu.its are shown in
In the Hart.ley and Colpitts circuits the necessary phase rela-
is obtained by connecting the grid and plate electrodes to the oppoends of the tuned or tank circuit; in the tuned-grid and the tuned
circuits the mntual inductance must have the appropriate polarity.
the tuned-grid-tuned-plate circuit, oscillations are obtained only whengrid tuned circuit LoCo and the plate tuned circu.it LpC. are both
usted to offer an ind ueti ve reactance at the frequency to he genera.ted.
arrangement can accordingly be redrawn as shown in Fig. 14-lf, and
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