IXTERMITTEXT BEHAVIOR L\ OSCILLATOR^ 



13 



promoted by increase of the Q of the tuned circuit and by decrease of the 

 time constant of the grid-leak-condenser combination. 



\'III. The Lamp Stabilized Oscillator 



The circuit of Fig. 16 is of particular interest because the functions of 

 ampliher, limiter, and filter are performed separately by units which are 

 readily identified with their functions. The present method of analysis 

 was developed in connection with this particular circuit. The output 

 frequency and amplitude are both quite stable and the harmonic content 

 of the output is low. 



Fig. 16 — Schematic diagram of lamp stabilized oscillator. 



Under operating conditions the gain of the tuned amplifier, which is 

 ordinarily in the order of 40 db, is equalled by the loss of the lamp bridge. 

 The lamps operate at such a temperature that their resistance is slightly 

 less than that of the associated linear resistors. If the gain of the amplifiers 

 is for any reason somewhat reduced, the current through the lamps decreases, 

 the temperature and resistance of the lamps is reduced, and the loss through 

 the bridge is reduced to the new value of amplifier gain. 



The d-c characteristic of a lamp bridge is shown in Fig. 17. A curv^e 

 identical with Fig. 17 is observed if the measurement is made with an alter- 

 nating current whose period is very short in comparison to the thermal 

 time-constant of the filaments. Up to L the operation is nearly linear. In 

 the region of M the output is essentially independent of the input. At N 

 the bridge is nearly balanced and a small percentage change in the input 

 voltage results in a large and opposite percentage change in the output. 

 It is thus seen that an alternating current having a small superimposed 

 modulation of low frequency will result in an output having a considerably 



