Tube amp question

I have an Allied Model 333 tube amp/receiver that has been working fine for some time now. All of a sudden, it has developed a noise/distortion in the right channel which is very noticeable. Is this the sign of a bad tube or something more? I use this amp when I listen to vinyl. Any suggestions? Thanks
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Try switching one by one each tube from one channel to the other and see if and when the noise/distortion changes channels. Then you'll know if it is a tube and which one.
Ncarcv is right on the money.
Is the channel still playing? If playing how's the volume lower, higher than healthy channel?
Do you have spare tubes? Just by swapping tubes you'll have a chance to destroy components around the tube on your healthy channel.
Make sure that channel still works at the same volume as the healthy one.