If you choose to play your vintage radio, please read this article. The information below is for the small (wood or plastic) AC/DC radios made from the early 30's thru the 50's.
I would strongly recommend that the tiny tube radios made from the early 30's through the 50's not be played more than an hour or so at a time. The reason; HEAT, these small and many of them quite valuable (such as the Charlie McCarthy pictured above), squeeze 5 to 6 tubes in a very small space and the heat generated can be damaging to the case, the finish and the internal parts. I have measured the internal temperature of some of these sets with the back in place at over 200 degrees after an hour of operation. These sets are generally collected for their appearance, not their sound quality. So to protect your investment, do play them occasionally but it's best not to allow them to operate for extended periods of time like you would a modern solid state radio. If you do choose to play your radio, make sure there is adequate room for proper ventilation so it won't overheat. Do not play it if stuffed into a tight cubby hole where air cannot circulate around it. If you enjoy playing an old radio all day long, make sure it has adequate ventilation and large enough to dissipate the heat properly.
On many of the small sets you may hear a slight hum even though the set was restored electronically, this may be normal as the circuits in some sets to filter out the hum were not very efficient and some speakers were more efficient in reproducing the hum than others.
When appliances cycle on or off or light switches are flipped, you may hear noise or static. The same conditions could also cause the volume level to change or you may hear more noise or static. This too is normal and will vary depending on your reception area and antenna. Nearly all small sets made up to 1939 required an external antenna and will perform very poorly without one. Computers and TV sets often wreak havoc with AM radios due to the RF interference they generate.
The bottom line is these tiny sets were made without much thought concerning heat, durability or sometimes safety. Many of those small sets that were played for hours on end simply self destructed and were subsequently thrown in the trash and many of the more desirable models are nearly impossible to find today.
Keep in mind that during the heyday of tube type radios & television, there was an army of radio and TV repairmen out there and there was a radio/TV shop on almost every corner. There was a reason for so many of these (now mostly gone) shops.
A NOTE CONCERNING SAFETY! many of these tiny radios can be a SHOCK HAZARD and even be lethal. Take care in operating these, some that were made in metal cabinets, can be DEADLY if the AC line is at case or chassis potential. When I restore these sets I install a "Polarized" line cord to prevent the shock hazard. Under no circumstances should the polarized plug be defeated. As mentioned above, many early sets require an external antenna for operation, NEVER ATTEMPT TO GROUND ANY RADIO MADE FOR AC/DC OPERATION or allow your antenna or ground wire to come in contact with any metal portion of the radio such as the chassis or screws that may be connected to the chassis. The antenna connection is usually a wire coming from the inside of the radio and is always isolated from the chassis to prevent a shock hazard. When servicing/repairing such radios always use an isolation transformer.
my companion article: Operating your vintage television