Sound Problem

[VA561]

I have a '55 Philco Model 4113. The tv has a great picture but has developed a sound problem. I watch the tv on average 2 hrs per week. Sometimes when I turn the tv on the sound is great at first with no problems at all. Then for no apparent reason the sound will will just fade away. I will watch the tv with no sound and all of a sudden it will come back again maybe 10-30 minutes later.
At other times I will turn the tv on and no sound from the beginning.
If I turn the volume control all the way up I just can hear the show but nothing if I turn the volume control to where a normal listening level would be. All advice would be greatly appreciated.