[Winky Dink]

Hoping for a quick answer.  In two hours I'm going to look at a Majestic Model 72 (Model 70 chassis, 7-A, 1928).
If the owner recalls this set being used 30 years ago, then I'm sure it's a 60-cycle set.  If not, is there a way that I can be sure it's NOT a 30-cycle set?  60-cycle sets used a 7-B-6 power supply; 30-cycle sets used a 7-B-3 power supply.  Where were 30-cycle sets used?

Thanks,
Henry