This stuff was usually easily adjustable, so you could compensate for various irregularities. But some turntables had built-in strobe lights for aiding in adjustments, so if the line frequency was off then the strobe would be off and then your adjustments would be off, too. And even if generally well-adjusted, should the line frequency vary too much while playing a record then you would probably notice that. During musical passages it would probably definitely be noticeable, while during singing and speech maybe not at all.