Try what Norm suggested with the other radio, and if that does not solve it, gently tap each tube, then gently push each tube to one side, as you may also just have a socket, or a tube pin that is corroded.
If that does not locate it, pull the chassis and check for cold solder joints, as I have found that on ocaission too, but if nothing is obvious, carefully power the radio up, and gently push and prod each capacitor (use a dowel, or something blunt and non-conductive). Usually the cap that is a problem is turned up by this.
If the radio had been stored outside, or saw any water damage at all, check for corrosion on the tuning condensor shaft too, unless you have tried turning the radio on with it tuned to very different stations with the same result as you have been having. My Setchell Carlson has this trouble, but does not always occur.
:When I turn on my RCA 10K I notice that when warming up it suddenly pops and the green eye closes suddenly (not all the way) and then I hear the station. I just wonder why the sudden pop and then instant audio as my other GE which is the same seems to warm up slowly and fade in as the green eye closes slowly and I hear the station fade in slowly. Norm if you read this I remember you telling me about the cathode coming loose could this be the same thing, you were right last time it was the 6L6...Thanx