This turntable has been running fine since the early 80s. Recently it developed, or seems to have developed, a ground hum on the left channel. It is signal grounded to the preamp using the ground strap from the turntable. The loop just presented itself one day out of the blue. If I unstrap the signal ground the hum is very loud. If I reverse left to right the problem transfers to the other channel so it is the turntable not the preamp.
SUGGESTIONS OR IDEAS?