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

George Brock-Nannestad wrote:
From: Patent Tactics, George Brock-Nannestad

Mike Biel wrote

Hi George.

We fought this out several times in the 78-L in past years, and someone might be able to come up with my more detailed answers.

----- thanks for the response that is as lucid as your replies are always!.

I only have a few comments.

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!

And even when it was, the frequency was not standardised. This obviously improved after Lamme wrote his paper "The Technical Story of the Frequencies" in 1918 (American Institute of Electrical Engineers, Washington D.C. Section, reproduced in "Electrical Engineering Papers" by Benjamin G. Lamme, Westinghouse Electric & Mfg. Co. 1919, pp. 569-
589), but certainly Great Britain had DC, 25 Hz, 40, 50, 60, 83 (44,000 persons had this!!) and 85 Hz well into the 1930s.
Another reason for the use of governors for electric motors. Victor had several different electric motors that you could select from.
Central Copenhagen (Denmark)
Is there another Copenhagen??
had DC until 1962.
I think NYC finally got rid of the last of the DC only a very few years ago. It was mainly being used for elevators.

I have seen a disc record stroboscope for use with an a=435 Hz tuning fork as a light modulator, which avoided the issue entirely.
I like the Sarasate method best -- record a tuning A on each record!
The universal instruction for Gramophone Company recording experts and engineers was to place a thin white slip of paper (cigarette or onion skin) under the wax and count (GC correspondence and interview with the Denmark-
based EMI recording engineer from 1936-45) for a minute, aiming at 78. This was in those locations that used the Hayes portable.
I like the American Columbia instructions of counting to 20 in 15 seconds better. Another reason why 80 makes more sense than 78. And Edison's slow speed of 30 instead of 33 1/3 -- one rev in exactly two seconds. They were grooved at 300 per inch, which means that it was 10 minutes per grooved inch. The tone arm (on the two playback machines that were made) had a micrometer dial for cueing. (And if we say 33 1/3 instead of 33, why don't we say 78 1/4 here in the West Hemisphere, at least?)
In Oslo (Norway) they had a synchronous motor, so the speed was 77.92 by default, if the mains was stable at 50 Hz, which it was not (hydroelectric with slow regulation).

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!

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.
I am glad you took the time
Hey! I'm retired! What else do I have to do? (Not really, I am still emptying my office and The Department Chairman From Hell is breathing down my neck even though he doesn't need the room.)

to comment on the other of Isom's failings - it is a necessary reference and comment, just like your previous one on Peter Copeland' papers.

Kind regards, George

It's my duty to do so. Remember what Joe Pengelly called me while I was doing reviews in the ARSC Journal -- Biel the Impaler! (But I am even more full of praise for quality work.)

Mike Biel mbiel@xxxxxxxxx

............ a lot stricken - see Mike's original post on 17 September 2008 in view of
the earlier from 15 September.
This is going beyond my original statement that strobe discs, not gear ratios, was the reason it is 78.26 and 77.92. But your question concerned Isom, and although much of what he wrote is good, this entire section on speed is bogus.

Mike Biel mbiel@xxxxxxxxx

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