As part of another tuner project here's some results from a 6BN6 for the FM discriminator. Its running at 10.7MHz IF. The output is around +/-4V pk for 75KHz deviation. I've used a double coupled tuned circuit to improve distortion. They are 10k toko coils with the turns/cap removed and 32T wound on each bobbin. The cap over the top was just twisted wire, but for an actual design a secondary winding of 4T would be wound on each coil and coupled with a bigger cap there. The coils require accurate adjustment but a THD of .3% is possible.
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The old timer's gimmick cap., excellent!
That nice 0.3% THD number is in line with the "propaganda" disseminated about FM demodulation methods that RC integrate a train of pulses. You've verified the low distortion claims.
That nice 0.3% THD number is in line with the "propaganda" disseminated about FM demodulation methods that RC integrate a train of pulses. You've verified the low distortion claims.