Here's a little tip I'd thought I would share.
Do you have an AC/DC all american five set with all capacitors replaced, with good tubes, that has low audio output with very garbled and distorted sound?
Focus on the audio circuit. The RF section is working since you are getting audio, and one common culprit I see is the plate load resistor off the 2nd detector/first amplifier tube. Examples are the 12Q7, 12SQ7, 12AV6, 12AT6 or 14B6.
If this resistor has drifted to a high value, a large voltage drop will occur across it, leaving little plate voltage, even as low as 3 or 4 volts and still pass a signal that will be amplified by the output tube.
Checking voltages and resistors is a good way to find troubles like these.
Canadian Vintage Radio Society