I'll have try our big toaster oven for tar-melting the next time my wife goes away to visit her sister. For this rebuild the last steps are to replace the condensers...
...and then replace the tar. That's just a piece of cardboard with some crumbled tar melted to a quarter-inch thickness.
Next I created a problem by fixing the problematic (noisy) volume rheostat. Found a used part on Ebay--different Bakelite color, but the same innards. Replaced the defective wire-wound resistive element and rewired it the same way as it was, but now it won't shut the volume down enough. The stronger stations are fairly loud with the rheostat in the starting position.
I'm sure I have it wired consistent with the schematic, the service manual description, and the original wiring. The manual says:
"...variable resistance connected between the antenna and ground posts of the set. When the knob is full 'on' the slider passes off the coil, cutting the latter out of the circuit entirely. As the control is turned back, less and less resistance is included between the aerial and the ground so that more and more of the incoming signal is shunted to the ground...thereby reducing the volume..."
But it doesn't reduce the volume enough. Here's the Atwater Kent schematic (for my "early" model without later additional connections for a shielded antenna cable) with my simplified version inset.
This is a snip from a modern schematic made in 2005 by W3NLB (stated for "all versions" of Model 37, but clearly different from the AK schematics).
What's wrong, and how do I fix it? Is it possible that I have chassis ground leaking some signal back into the RF amplifiers? I could rewire it according to W3NLB's schematic except for the center tap on the antenna choke.
Hoping for suggestions.