Zenith R721...please help!!

I'm an amateur, but love old radios. My Zenith R721 has great tone and reception. However, the volume gets very loud and low by itself, and often. Is this a tube problem??

The first thing to try is remove the tubes and reinsert, as you may have a tube socket that may need cleaning. As you remove and replace it in its socket it may wipe off any corrosion present. It could be as the radio warms up, it could have either a tube or a component that may be breaking down or a bad solder connection that expands and contracts under heat. Try removing the chassis, and using an insulated piece of plastic (like a pencil shape) and lightly tap different parts to see if when you tap it it changes volume. If so you have found the part that is either defective or needs re-soldering.

Thanks, I'll try that, and post my results...please stay tuned!!