Another question comes to mind. Did you re-build the amplofier? The old caps are leaky, and could conceivably be causing your immediate problem. I'd re-cap whole thing, and put in neww electrolytics, as well, to bring power aupply up to full potential......
Now, as for quality, how well is it actually playing? If un-rebuilt, it can't be great. Some people think that if it "makes noise" it's doing great...As for me, Knowing what the full potential can be, I opt for bringing them back to factory specs.
So, let's all have fun with "our toys". But, as when younger, these gems of the past need proper maintennance.