1920s battery radios....how do they work?

[Kamakiri]

Decided to take a leap backwards in my learning and try to understand how a 1920s battery radio works....and thereby learn to repair them and even soup them up a bit if possible

Let's take this 1925 Resas Tone-A-Dyne.....I now have two of them. Since I can't seem to get any form of schematic on it (and even if I could, 1920s radio schematics are horrible compared to the Sams I've been spoiled on using with TVs), I'm having some difficulty understanding how the radio works.

Let me start by saying that I do understand the A, B, and C voltages and what they do, and both radios do work. They use five 01A tubes. No real parts inside except the coils, two transformers (no idea what they do), and one plug-in 1.5 meg grid leak resistor (again, no idea what it does).

Resas #1 works fine, but the volume and frequency tend to drift around a little and it requires adjustment every few minutes. Resas #2 is much more stable, but the audio is more muffled. Since I operated both on the same set of 01As, this leads me to believe that there are components I can replace to get them performing better.

The 1.5M grid leak resistor on Resas #1 measures 2.6M, so that needs replacing. The one on Resas #2 measures out at 1.7M, so that's closer. What a grid leak resistor does I'm not sure.

Picked up a restored Atwater Kent big box model 20, and that thing makes the Tone-A-Dynes sound like the dog's blanket....so either the A-K is just a superior radio, or the Resas(es) need work.

Incidentally, I started figuring out how to tune them by hooking up a signal generator and dialing them in with it, then cutting the power when I found the desired frequency. Since all of these radios seem to love being hooked up to the signal generator and get much better reception when hooked up to it even when it's off, until I get a larger antenna I just run them that way

Any insights and advice are always appreciated!