THE BRIDGE STABILIZED OSCILLATOR 



585 



The particular value assumed by Ri in the circuit of Fig. 3 is ap- 

 proximately (R2Rz)/Ri = [(100)(150)]/114 = 131.6 ohms, and hence 

 from Fig. 5 it follows that the power supplied to the lamp is about 3.7 

 milliwatts. The r.m.s. voltage across the lamp is computed to be 

 0.70 volt, and across the entire bridge, 1.23 volt. The power supplied 

 to a load of 150 ohms through the pad composed of R-; and Rs is accord- 

 ingly 0.22 milliwatt, or 6.6 db below 1 milliwatt, which is in agreement 

 with measurements shown in Figs. 8 and 9, described below. These 

 quantities are given to illustrate the fact that currents and voltages in 



60 80 100 120 140 160 180 200 220 240 260 



PLATE BATTERY POTENTIAL IN VOLTS 



Fig. 6 — Oscillator frequency vs. plate battery potential. 



a — Ci and C2 tuned for maximum amplifier gain. 

 b — Ci and C2 decreased 5%. 

 c — Ci and Co increased 5%. 



this type of oscillator may be calculated readily from the values of the 

 circuit elements, and without reference to the power supply voltages or 

 the tube characteristics except to assume that they give the amplifier 

 sufficient gain to operate the bridge near balance, and that tube over- 

 loading does not occur at the operating level. 



Experimental performance curves for the circuit of Fig. 3 are pre- 

 sented in Figs. 6 to 11 inclusive. Figure 6 shows frequency deviation 

 plotted against plate battery voltage for several settings of the grid 

 and plate tuning condensers. For curve a the amplifier was adjusted 

 at maximum gain, corresponding approximately to zero phase shift as 



