Audio -- Welcome to AK! You'll find plenty of great folks here to help you with any issues you have with your receiver. Most have direct experience, and have worked on their own units to gain that experience.
If with a good antenna the unit is still displaying problems, then check to see if the Stereo Beacon lamp comes on when the front panel selector switch is set for FM Stereo (not Automatic). This is a forced stereo setting. If the lamp doesn't come on in this mode, then likely the bulb is burned out, or, the relay contacts controlling the lamp are dirty.
If the lamp does come on in the test above, then next determine if the the sound quality and tuning characteristics are still poor when set to FM Mono. In this mode, the signal bypasses the MPX sub-chassis so that you are listening directly to the tuner. If the sound quality is still poor, there is still some intervening switching circuitry between the tuner and the audio section that could be the issue, but more likely, it is the alignment of the tuner itself. Regardless of the condition of the switching circuitry, if the tuning characteristics are still poor when set for FM Mono, then the tuner section will definitely need attention.
The tubes directly dealing with the tuner include the 6HA5, 6CW4s, 6HR6, and 6AU6s. The Stereo MPX section tubes include the 6GH5, and three 12AX7 tubes on the MX-65 sub-chassis. The remainder of the tubes make up the phono, tone control, and audio power amplifier sections of the receiver.
I hope this helps!
Dave
