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"Copeland, Peter" <[log in to unmask]> wrote: 

>    When discs were mastered on wax, a small degree of runout-groove was
>cut as the song (or whatever) ended, and then the cutter was raised from
>the wax. Here in the UK, this runout-groove may be seen on His Master's
>Voice acoustically-recorded 78s in late 1924 and early 1925, followed by
>a *con*centric to catch the reproducing needle before it ploughed-up the
>label.
>    After about March 1925, the wax would be taken to a factory well
>away from the actual studio, where it could then be loaded onto a
>machine dedicated to cutting eccentric grooves. 

Here in the US, the situation was similar with The Victor Talking
Machine Company, yet slightly different.  In the earlier acoustic days
there was no runout groove - the record groove continued for a few
turns after the end of the song, then the cutter was lifted from the
wax and a concentric groove was cut just outside the label area.  The
weight of the reproducer would carry it from the suddenly-ended
recorded groove into the concentric groove.

The Gramophone Company, in some of its early wax recordings, did cut a
very fast-moving spiral-out groove to take the reproducing needle to
the concentric groove; to my knowledge Victor never did this, although
when pressing Gramophone records for the American market Victor did
not remove this groove from their pressings.

Starting in the early 1920s, Victor began using a double eccentric
groove in tandem with an automatic braking mechanism.  The size of the
double eccentric groove was varied to fit the diameter of the dead wax
just outside the recorded groove area.  I have wondered for some
thirty years how they did that, because it seems more complex than
just an off-center centering of the wax on a special lathe - the
diameter of the eccentric varied, being larger if the recorded groove
was farther away from the label.

There was no spiral-out on these - after the song finished, there was
a very small bit of runout...almost as though the turntable was slowed
down for a fraction of a revolution while the cutter continued at the
same speed.  But what is interesting - and seems sort of pointless -
is that Victor cut an additional concentric groove just outside the
recorded material.  This groove BREAKS to permit the runout portion to
exit. Why this was added is anyone's guess, but it stayed on until
Victor switched to a spiral-out system in the mid 1930s. The broken
concentric continued with Victor's low-priced Bluebird label, which
did not abandon the double-eccentric until the early 1940s.

Why a double eccentric groove was used in the first place is a mystery
to me, but I did notice that on my Victrola XIV the brake setting
mechanism had a little bit of "play" - if you used the inner eccentric
to set the brake, when you actually started the turntable the
mechanism moved just a fraction of an inch....the exact distance
between the inner and outer eccentrics. The reproducer needle would,
of course, be "picked up" by the outer eccentric, but apparently the
inner eccentric was used to actually set this point.

Victor is the only US label, to my knowledge, that used an eccentric
groove during the 1920s, and my guess is that it was part of their
patent on the brake system.  Other labels, such as Brunswick and
Columbia, used a spiral-out groove that terminated in a locked
concentric groove, just as in a modern LP record.  Other labels
adopted a combination of a spiral-out leading to a double or single
eccentric groove at various times during the 1930s. Captiol records,
which began in 1942, used an eccentric spiral-out for several years,
and Decca had an eccentric spiral on its early US recordings before
switching to a concentric spiral. (Incidentally, most US Deccas quite
clearly show that the runout spiral and eccentric groove - which has
precious little eccentricity to it - were cut on a different machine
from the recording machine.  The groove is considerably deeper and
thicker than the actual record groove.)

The eccentric runout groove remained standard for the early years of
the long-playing record as well, with some labels using it right up
until 1957 or 1958.  By 1960 I think all major US labels had settled
on a concentric, rather than eccentric, groove.