@Austin_Dern it'd be a 108:1 gearing on a similar synchronous motor to get 33⅓ exactly
and 108 is conveniently easy to break down into multiple gear stages, you could even go five stages with 2:1, 2:1, 3:1, 3:1, 3:1 though i imagine something like 9:1, 12:1 or 3:1, 36:1 would have been more likely if they did that
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@Austin_Dern it also turns out that a simple 80:1 gearing gets you 45 rpm from a 60 Hz synchronous motor
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@Austin_Dern oh 33⅓ also works out nicely at 50 Hz, since the same motor on 50 Hz power would give you 3000 rpm, and you can gear that down to 33⅓ rpm with a 90:1 gearing
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@Felthry Yeah, there's some little differences you get between 50 Hz and 60 Hz power supplies and now I wonder if listeners in different electrical zones just got used to songs sounding a tiny bit different. The way that there (used to?) be a little PAL speedup to US-made TV shows.
There's shows I watched in Singapore with theme songs that just sound *sluggish* when I hear them now.
@Austin_Dern synchronous motors are only able to run at integer fractions of the supply frequency, so at 50 Hz you get 3000 RPM on a two-pole motor, or 1500 on a four-pole machine, or 1000 on a six-pole one...
and at 60 Hz you get 3600, 1800, 1200, 900, and so on
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@Austin_Dern to control the speed of a synchronous motor, you have to change the frequency of the supply voltage, which certainly can't be done with 1940s tech though it's easy today
other types of motor don't work for this because their speed is variable; induction motors and DC motors both slow down when they have more load on them and you can't control the load
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@Felthry Yeah, there'd really be no practical way to make a 'universal' record player that kept to a constant speed, not unless you also swapped out a gear inside. Probably easier to just accept stuff sounds a little different on different sides of the Atlantic.
@Felthry Very plausible, yeah.
45's, that got picked because the RCA engineers were told to do anything as long as it wasn't compatible with 33.