[Ron Ramirez]

+1 what Phlogiston said.

I've never seen a Philco that had the frame of the tuning cap isolated from ground and tied to the AVC bus instead. Every one I can recall at present from 1931 on had the tuning cap mounted on rubber, but the frame was still tied to ground, either by a wire soldered to a rotor connection on top (in sets such as the 70, 90, 71, etc.) or by one or two wire braid straps with one end soldered onto a tuning condenser mounting bolt, and the other end connected to the chassis, usually with a rivet.

In most Philco superheterodyne radios, AVC was applied to the RF amp (if used) and the 1st IF tube. Many Philcos did not have AVC applied to the mixer stage, although some did. And there are a few that did not have AVC on the IF stage, or if more than one IF stage, there was no AVC on the second IF stage.

In the Model 60, AVC is applied to the mixer stage as well as the IF stage - but the AVC goes through the secondary of the antenna coil, on the stator of the antenna stage of the tuning condenser, to grid 4 of the 6A7. The stator is the stationary, ungrounded part of the tuning condenser, which is insulated from the frame. The rotor is the part that rotates (hence the name rotor), and is physically connected to the tuning condenser frame.