Re: ND6T AGC Troubleshooting

Don, ND6T

I'm just sorry to hear that it isn't working for you. From your description it all seems correct. It would be nice if there was some substantial signal that you could tune to, something steady and strong. If you had a signal generator or some local signal source that you could tune into the audio pass-band then that would help. Barring that, a good AM broadcast signal, even WWV, would be nice. Use the carrier as the tone. I have usually obtained about 3 volts or more (at the point where you are testing) with a strong 1 mv signal. That mosfet needs a half volt to begin to conduct and if you aren't getting that there is a problem. A strong signal should be measurable at the high side of your volume control when using a DVM on the AC scale. If you can get that, then you should be able to walk it back up the AGC circuit and see what is going on. Yes, the Q1 bias is about right and the forward barrier voltage of your diodes are in the ball park. Maybe a short, open, or faulty component. -Don

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