Improving AM radio reception of weak stations

[wa2ise]

Using 2 diodes for the 2nd detector, one for the audio signal, and the other for the AVC circuit. A reason for separating these is to keep the AVC filter cap from backbiasing a single detector diode, which would cause clipping distortion on weak stations.

While I'm at it, I used a low voltage drop diode for the audio signal detection. An old fashioned geranium diode would work, or a Schottky diode. Not all Schottky diodes will work, if you do what I did, raiding the jubkbox and selecting diodes based only on a low reading on the diode selection of a DVM, you should try several different diodes to get one that works well. Do that by touching the diode leads to the radio detector circuit where the diode would belong, when it's powered on, tuned to a weak station. The original detector diode now serves as the AVC circuit source. Someone like Catman who knows lots on AM detectors would know which kind of Schottky diode to use.

[Kevin Kuehn]

I thought 6H6's were used in this fashion way back in the day, no?

[wa2ise]

Yes, and AA5s' 12AV6's also have two diodes. Probably didn't cost all that much more to put the 2nd diode in those tubes, and the diode electrodes also held the triode in position inside the tube. But most AA5 radio makers didn't use both diodes, just randomly choosing one or the other. Which meant that tube manufacturers couldn't delete a diode. They didn't want to spend the extra couple of pennies for an extra resistor and cap.