Problem with shifting volume: Zenith K-731

[Nolan Woodbury]

Over the last few days, one of my favorite sets has developed a problem.

Once warm and playing for 5-10 minutes, the volume will suddenly increase (with, it sounds like, an audible increase in treble too) and if left unattended, will eventually drop to, or perhaps lower than the original level. It isn’t (I don’t think) a reception issue, as the Zenith exhibits the same behavior on weak or strong (FM) stations. It just occurred to me I haven’t tried it on AM, so perhaps I’ll do that before reaching for the toolbox.

Could it be a voltage issue? A failing volume pot?

I'm set to pull the chassis out and have a look, but if this is a common problem perhaps one of you can provide a short cut. I began using this radio out of the box and it plays somewhat regularly. Because of its tone, it's a unit I'd like to keep and listen to more.

Awaiting the collective wisdom of the group to rain down upon me...