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High-output oscillator

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The circuit shown in Fig. 1 provides a higher output than is normally obtained from a Franklin oscillator. I found that the 6AW8A tube performed best in the circuit and that other triode-pentode tubes, such as the 6AX8, did notdo so well. The 27 pF capacitor C3 has a critical value and, if made any larger, produces squegging. When connecting the cathodes to ground, connect the lead first to Pin 1, then through the center socket sleeve to Pin 6, and then to ground. With the tuned circuits L1C1 and C2L2 tuned to 80 meters, the output voltage measured about 40 volt r.m.s. across a 22 kΩ load. When tuning L2C2 to 40 meters, the output voltage measured 15 volts r.m.s.

Fig 1
Fig. 1. Modified Franklin oscillator. Unless otherwise indicated, capacitances are in pF, resistors are ½ watt.

Oscar F. Forth, W3GYR.