[mikethedruid]

One thing occurs to me. You said that the Philco 6A7 tubes work well in your radio, but the RCA 6A7 does not. My question is, are the Philco tubes 6A7G, or 6A7GT type tubes, and is the RCA a plain 6A7 METAL tube? If so, that may well explain your problem. Check the wiring going to pin 1 in the chassis, not just the schematic. It should be tied to ground if the RCA tube is going to work OK, but sometimes Philco used it for a tie point for other things, since the 6A7G does not have a connection to pin 1 internally. The RCA 6A7 uses pin one to connect the metal outer case of the tube, and use it instead of a separate tube shield. Rule of thumb on Philcos, if the tube layout sticker, or the schematic call for a G type tube, use a G or GT type tube, and use the physical tube shield if there is one for that tube.