Most likely bad caps. The paper types become leaky and short. Your tone control will have a couple caps. (Music/speech is actually a tone control.) Change these caps to start but others may also be leaky.
Norm
: Hi, I just found a 1937 RCA Victrola for 80.00 Can and I tested all of the tubes and 2 were bad so I replaced them plus the filter caps and it works. Now I only notice one bad thing and that is sometimes I turn it on and the radio is loud so I only need to keep the volume on about 2 and it sounds great but then after it heats up for a while then it pops down to about half the volume. Then as I listen to it for a while sometimes it pops back up to the original louder volume level. Also I am not so sure which volume level is the "right" one. The music speech control has 2 settings normal and low boost. The normal is always the same but when the volume pops up in the boost position it is alot louder that the normal but when it is down the 2 settings are about the same just that one is more bassy than the other which is what I would expect.