[MrFixr55]

Hi Captain Clock,

I have a similar Zenith AM / FM that does the same thing. Have had it for 50 years, but haven't got around to fixing it. Did get a schematic finally when I bought a similar set.

Try the ol' divide and conquer technique. This set has a Radio / Phono switch. Connect a signal from an external audio source such as an MP3 or CD Player to the Phono jack and put the Radio / Phono switch into Phono. If the sound is still garbled, then the audio section is at fault. This is a much easier section to troubleshoot than the RF section!

!!!!!!!!!!!!CAUTION!!!!!!!!!!!!
This is a HOT CHASSIS Set, not a warm chassis set, meaning that one side of the line is connected to the chassis. This is done through the power switch! Therefore, if the chassis is connected to neutral through the power switch, the chassis poses little danger when the switch is on but is extremely dangerous when the switch is off. This is because the chassis becomes hot through the unswitched side of the power line through the tube heaters which have very low resistance when cold. Use a battery powered input source!

See the following link:
https://antiqueradio.org/safety.htm

If the issue is in the audio section, review the schematic. There is a feedback system in this radio involving feedback from both the output tube plate and a transformer winding to the low end of the volume control. Test by shorting the 1K resistor and disconnecting the feedback circuit and tone control. If this solves the issue, then troubleshoot the feedback circuit. Replace the 1K resistor between the volume control low point and chassis ground.

Hope this helps!