[Radioroslyn]

Well actually this set IS a superhet. It's a superhet with a regenerative detector. The 4 M resistor is the grid leak for the detector. By varying that value it will vary the selectivity of the detector. The high the value of resistor and the lower value of grid leak capacitor will give the max selectivity (sharpest). Average values are 1M and 100pf which is good for AM reception.
As Bill mentions there is no AVC. Regenerative detectors are very sensitive they don't like strong signals as they tend to overload easily. That's why the volume control is across the antenna to keep the signal low before reaching the detector stage. When it overloads the station it is tuned to will seem very wide. It will take up a lot more space on the dial than a weak one.
Regens make great one or two tube receivers, the detector with a stage of audio after it. Have built a few over the years and I'm always amazed at how well it works for just a tube or two.
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Terry