[GarySP]

Oh boy, nothing is more frustrating than intermittent issues. Try wiggling each tube in its' socket. Loctal tubes are notorious for poor contact with the thin pins. If that does nothing, try tapping different components with a chopstick and listen for changes in the static. You could also re-flow all solder points underneath the chassis to eliminate a possible cold joint. Pay very close attention to the condition of the wiring in the chassis. Rubber insulation breakdown could cause an intermittent problem. Check the easy stuff first, then work your way up. Good luck! Take care, - Gary