I have a Dual 503-1 turntable ,from a thrift store ,with no manual. There seems to be no way of adjusting the speed, and it ran at about 33.8 with the first belt. I got a thicker new belt (.025 thickness)that makes it run at 32.7. Would this be the only way to adjust speed,by varying belt thickness? Manuals seem to be non- existant.Did Dual make this turntable($350, 1991) with no speed adjustment?