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Re: [ARSCLIST] New online publication: Manual of analogue audio restoration techniques, by Peter Copeland

From: Patent Tactics, George Brock-Nannestad

Mike Biel wrote (a lot omitted here from the original response):

> >
> > 1) AC, which is the prerequisite for stroboscope (and induction motor)
> use, 
> > was by no means universal. 
> Which, of course means that an electric motor couldn't have been used at 
> that location either!

----- well, this is where the universal motor comes in. Like in vacuum 
cleaners, it will work off both DC and AC at any frequency. The construction 
with worm gear and the centrifugal governor on the faster moving motor shaft 
was a very compact one.

> >
> >   
> If the mains frequency was off, that would also fool the strobe disc, as 
> well as those who use AC hum sound to set the playback speed!

----- in radio work, duration is everything, so you had to trust your 
timings. At Nordwestdeutsche Rundfunk, in the early 1950s they installed a 
separate power mains supply for tape recorders and turntables that was 
crystal controlled to 50 Hz. This way they were quite independent of any 
mains, and their own hum may be relied on (I suspect there was very little)

> >
> > I would be very interested indeed in a precise reference to a 1920s use of
> > the stroboscopic disc for turntables.
> >
> >   
> The closest I've gotten to this is the strobe disc itself that Victor 
> Talking Machine printed.  There are mentions in the early 30s.

----- well, that does not really answer my query and casts doubt about the 
reasoning that the strobe disc came in the 1920s before the use of a 
synchronous motor for recording machines to lock to 78.26

Kind regards,


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