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Post by ScottPost by Liz TuddenhamPost by ScottWere all 78s shellac or could other materials be used?
By far the greatest number were pressed on 'Shellac', or 'Solid stock',
which is mostly slate dust and other abrasives held together with a
binder of shellac. In the early days the groove profile wasn't clearly
specified (the very first ones were etched with acid) so the needle
point had to be ground down to fit the groove on each individual record.
An astounding variety of other materials were tried at various times,
ranging from solid chocolate to cellophane on cardboard. One of the
most successful 'laminate' records used a core of coarse rubbish
(including cotton flock) with surface layers of extremely finely-ground
'shellac' compound for the grooves. 'Direct cut' discs were cellulose
nitrate varnish on an aluminium base, but scarcity of aluminium during
WWII led to galvanised steel and glass being used as substitutes.
Vinyl was too expensive to use before the days of microgroove records,
but the very last 78s were pressed on vinyl because the machinery to
make and press solid stock had become uneconomical for the small
quantities needed.
Thanks. The last paragraph is what I wondered. My grandfather had a 78
rpm turntable and I *thought* I had seen a vinyl disc (but it was a
very long time ago). My parents said you had to replace the stylus
after every play. Is this correct?
If you were lucky enough to find a vinyl 78, you would play it with a
lightweight sapphire or diamond stylus. These were 'permanant' styli
and took a long while to wear out. The same stylus would play 'shellac'
records but, because it didn't wear to fit the groove section, it
didn't give good results on older records (later records had
standardised grooves that suited the stylus).
Most 78s are cut with 'coarse' grooves whereas later records (45 and
33+1/3 rpm) are 'microgroove'. Two different styli are needed and these
were often arranged on opposite sides of the cartridge, which could be
turned over to select the required stylus. Another system had them on
opposite sides of a lightweight bar which could be rotated. Philps had
them side by side, so the head was rocked to select them, Decca had two
completely separate plug-in heads and most later American manufacturers
had little plug-in carriers that had to be interchanged. A whole range
of custom stylus sizes is available for playing older 78s correctly, but
they are individually made and very expensive.
Needles were available in steel, fibre (bamboo) or thorn. Because they
wore down, they had to be replaced at each playing. A steel needle with
'flats' worn into it by one groove shape could do a lot of damage if it
was re-used in a groove of a different shape. You were lucky to get a
fibre or thorn to last more than 4 minutes, so you had to either keep
replacing them or sharpen them between records with a little gadget.
Some electrical pickups that used needles relied on the needle acting as
a magnetic armature - there are many stories of operators caught out
when they accidentally used thorns or brass tacks.
There were discs made of 'filled vinyl', which was vinyl with a lot of
abrasive in it. These were used for broadcast transcription, for
distributing programmes to remote transmitters and the internal
broadcasting systems of military bases. The advantage was that they
were lighter than shellac pressings for air freight and almost
unbreakable, but could still be played on existing equipment with a
needle in an electrical pickup. Some of them were 16" diameter, so you
would have difficulty playing them on domestic equipment.
For early film soundtracks there were 16" solid-stock discs with
vertical modulation of the groove. They started at the centre and
played outwards, with a little pit at the beginning, which the operator
placed the needle in. Having positively lined up the disc on the
turntable, he lined up the film in the projector to a marked frame on
the leader and then coupled the two machines together with a clutch.
From then on, they were supposed to stay in synch. Because the discs
were so large, they could be recorded at 33+1/3 rpm to give a reasonable
surface speed without too much loss of sound quality and would last for
one reel of the film.
--
~ Liz Tuddenham ~
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www.poppyrecords.co.uk