Studio 22+ sound/effects loop? problem

[Ibanez666]

Got a Studio 22+ today and I played it for 30 minutes then all of a sudden the volume went down and the sound became thinner. I read something about the effectsloop problems, so I decided to put a cable to connect the in and out of the loop and the original sound was back again. After a while I took the cable out again, and the sound remained the same..

what may cause this? A bad tube that malfunctions when warmed up? If so, which one should I check?

thnx

 

[MrMarkIII]

Some times the loop jacks need to be worked. A thin layer of corrosion can build up when they are not used for a long time.