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From: Patent Tactics, George Brock-Nannestad

Trey Bunn wrote, and John Ross and David Lennick have already answered most 
of the queries.

However, classification-wise there are aluminum discs pure and simple, but 
this is not one of those. The aluminum discs were pre-grooved, Fairchild were 
among the first to make embossing equipment for recording on them, and they 
have to be treated very differently from the thing you have, a lacquer disc.

If aluminum discs have been played with heavy soundboxes or pickups they are 
almost ruined. I have spent 8 hours correcting derailings under the 
microscope on one 10" record side by simply massaging some edge back to re-
create groove walls. This embossable aluminum is incredibly soft and 
malleable under the microscope.

As to the lacquer discs (sometimes erroneously called 'acetates'), the 
recording turntable had to struggle real hard to rotate the disc at the 
proper constant speed when it was cutting, and you needed not just the center 
pin for centering, but it was threaded, so that you could use a nut to clamp 
the centre to the turntable. If that was not enough, the turntable had an off-
set pin that went through one of the other holes, so that it did not slip at 
all. For reproduction that was unneccesary.

Kind regards,


George


> I have a 10" aluminum record with the brand name Perma Disk that I
> need to digitize.  It has three holes (two in addition to the standard
> center hole) and instructions on either side to "play outside in" and
> "play inside out."  Although the turntable I have isn't
> bi-directional, recording it backwards and then reversing the sound
> wouldn't be difficult.
> 
> What I'm wondering is whether or not the equipment I have will work.
> I have a stylus for playing 78s (the disk is recorded at 78 speed),
> but that's for shellac disks, and I assume that there's a different
> stylus for aluminum.  There is also one that I just found in a cabinet
> (this equipment was purchased long before I started working here) that
> says it's "2.7 mil, 78/transcription."  Would this be the right one
> for the aluminum disc?  And are those other two holes really
> necessary, or can I use the turntable we have?  If I do need a new
> stylus for this, can anyone recommend the proper one and where to get
> it?
> 
> Actually, I'm not even 100% sure this is aluminum.  The disk is black
> like an LP, but the edge is metallic colored.  I found a picture of
> the label at http://www.phonozoic.net/recordio/ (about 1/4 of the way
> down the page), and it appears that this company made disks of glass,
> steel, and simply "metal" in the third example (which most closely
> resembles the one I have, but my label is blue).  Anyone have any
> insight?
> 
> 
> Thanks,
> 
> ---------
> Trey Bunn
> Audiovisual Conservator
> Emory University Libraries
> Preservation Office
> Atlanta, GA
> 404-727-4894