We repair vintage tube radios. Many tube radios that have not been used for many years have capacitors that have "dried-up" and may cause the radio to hum or not function at all. We often can rejuvenate the capacitors by applying a controlled voltage that will restore the capacitors to working condition over a period of days. This rejuvenation will prevent the necessity of replacing all of the capacitors thus keeping the radio more original. Many collectors would prefer that the capacitors not be replaced with modern capacitors.
People often feel that the tubes may need to be replaced because they are very old, actually the tube elements are in a vacuum and can last almost "forever" when not used. The tubes may be the parts least likely in need of replacement if the radio has not seen heavy use.