Cool! Hope you get it working,

Same here, I probably only use my B&K 520B a couple of times a year and have found some bad transistors with it on several occasions over the years. Thanks for watching and your comment.

Thanks Frank!

Lubricate the RF gain potentiometer with contact cleaner spray. The band switch contacts might be dirty or corroded. This can affect AM reception. Try cleaning the band switch contacts using contact cleaner spray. Capacitors and Transistors in Zenith radios from that era generally have good capacitors. However, if the radio was stored in a damp environment, the capacitors could become leaky, affecting volume. Try removing and reinserting the socket transistors, clean the pins and use the red deoxIT on the sockets. Might be the oscillator transistor. One easy way to check that your LO is working is to place another radio next to your TO, with the dial at a blank spot near the top of the dial. Then put the TO on the AM/BC band and tune around between 1100 and 1200 KHz. If you hear the noise level drop significantly on the other radio, your LO is working. If you’re hear nothing on the AM band except when the BFO (Beat Frequency Oscillator) is on, it suggests that the IF (Intermediate Frequency) string is working. However, either the RF amplifier or, more likely, the LO (Local Oscillator) is not functioning. The oscillator transistor could also be defective. The FM RF and oscillator transistors are the same, number 121-687, I think. Swap them and the AM should work, and FM will not work. The oscillator transistor might be bad. Good luck!

Thanks so much for the response...Looks like I have some work to do. I'm new at this but will take it slow.@@kenslab1973

Robert, No, you do not have to remove the chassis in order to replace the 2 dial bulbs in the dial tube. All you do is naturally remove the battery cover and then remove the 3 back cover screws on the bottom, when removing the back cover being careful not to pull it out too far until you disconnect the antenna lead, the tuner RCA plug and the 3 prong plug that connects the 12 volt and 1.5-volt batteries to the radio. Turn the band selector switch in the location where you’ll see the copper plate on the dial drum. You’ll need a socket (standard) with perhaps an extension to remove the 2 screws; you’ll then have access to the dial bulbs. In the bottom right area of the back cover that is just for the dial lights and the chart map bulb. It’s just a single D battery that operate the lights. Hope this helps. Thanks for watching.

Thanks Ken for the prompt and complete reply. The chart light looks straightforward…unscrew and replace. This looks like a job for small fingers…not my big mitts…cheers…