This has several vacuum tubes and those are suspect. Take a pencil and tap the glass of the smaller tubes to look for noise changes. You may have to take off the tube metal shield to do this.
If you have got 15 years of life from the tubes that is great. Also suspect are electrolytic filter caps.
If you are not electronically adept, take it in for repair.
Tapping on old tubes is not a good idea. The glass is thin and very fagile. If you break it the results could resemble fireworks. If you don't have a tube tester unplug the set and check for loose tubes and bad connections. Plug the set back in and look for a blue glow inside the tubes. This would indicate there is air inside the tube. Check to see if all the tubes show a red glow from the heating element. If you can't find the problem, refer the set to an old tube puller ,like me , who has a supply of tubes and a tube tester. Old electronic radios,amps ,ect are far more dangerous to work on than new ones.Be careful. "The Tube Puller" [email protected]
For reference, a "blue glow" INSIDE a vacuum tube is indication it is "gassy", not that air has leaked. An indication that air has leaked is if the silvery getter inside has started to oxidize and turn white instead of silver. Tapping tubes with a wood pencil gently will not break the glass. Many tubes have two heaters and just seeing a glow inside is NOT enough. One has to look for a heater glow (orange, not red) for each section of tubes that have multiple sections such as 12AX7's, etc. I have worked with tubes for 55 years and MANY types including recieving and transmitting. Tube testers are indication only and some do a poor job of verifying the condition of a tube. Some are better than others.
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