[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

[KCMike]

I'm sure someone here can give you more details on cycle difference. I think you can run 30 cycle on 60 cycle. Here is a thread that might help you since you need quick answer.
http://antiqueradios.com/forums/viewtopic.php?t=101407

[Winky Dink]

Thanks. A quick look at the antiqueradios.com post indicates that it'll tell me everything I'll need to know.

[Eliot Ness]

You might be thinking of 25hz instead of 30hz.  25hz was used around the Niagara Falls area and the transformers are easily recognized because they are larger than their 60hz counterparts.  Fortunately a 25hz transformer will run just fine on 60hz power, in fact it will run much cooler because it is larger (more iron).

[Winky Dink]

The service manual specifies 60-cycle and 30-cycle models with slight differences in the power supplies. I've seen several other radios of that era that offered 60- and 25-cycle models. The cities (and even small towns) in my area--Southern Idaho--all had their own commercial power companies, so I guess they chose whichever worked best for them.
I didn't realize that a radio could use either type of current with, at most, minor modifications to achieve the best performance.

[morzh]

Both 25-30 and 60Hz sets can use 60Hz, not other way around. You need a heavier core to use at 30Hz and possibly more turns. But go up in freqjencies and you have more reliable heavy part for free. Of course it's a back breaker.

[Winky Dink]

Your advice is duly noted.