Design Example - Audio Oscillator

Circuit of Fig. 152, with 6C5 tube, E_B = 150 volts, E_c = -10 volts.

Frequency 800 cycles.

Plate load impedance = 20,000 ohms.

Class B operation; grid swings to +2 volts.

Average power output = (115 · 5.6)/4 = 160 mw.

Transformer voltage ratio P/G = 115/12 = 81/8.5 rms.

For low harmonic distortion, volt-amperes = 10 · tube output =1.6 v-a.

Current in plate winding = 0.02 amp.

Core is the same as in Interstage Transformer.

Primary 2,100 turns No. 32 enamel. Winding resistance = 125 ohms.

Grid 250 turns No. 42 enamel. Winding resistance = 180 ohms.

l_g = 0.060 in., l_c = 4.5 in., A_c = 0.32 sq in., core weight = 0.4 lb.

From Fig. 140 core loss = 0.2 · 0.6 · 0.4 = 0.048 watt.

Gap loss   = 0.030 watt.

Primary copper loss = (0.02)² · 125 = 0.05 watt.

This leaves 32 mw available for secondary output.