CED Digest Vol. 3 No. 19

CED Digest Vol. 3 No. 19 • 5/9/1998
Date: Thu, 07 May 1998 02:05:33 -0700
From: Tom Howe
To: ceds@teleport.com
Subject: RE: belt size for sgt100?

The flat neoprene belt that drives the turntable in RCA's F and G players has an
inside diameter of 21.8" and a width of 0.187". The FR21.5 belt from PRB is the
nearest stock equivalent that will work fine as a replacement. This should be
available from any repair shop that carries PRB belts, which is the name brand
most widely stocked. This belt will also be available from CED Magic for $2 when
I get the Belt Replacement Guide completed in about another 3 weeks.

--Tom Howe
http://www.cedmagic.com 

------------------------------------------------------------------------
Date: Sat, 09 May 1998 12:15:17 -0700
From: Neil Wagner 
To: *CED Digest <ceds@teleport.com>
Subject: Videodisc History - Part 24

>From the August 1982 Popular Science -

Optical disc can store an encyclopedia - Part 3
                   by John Free
------------------------------------------------------
New recorders capture images, computer data,
or audio for instant playback
------------------------------------------------------

[Sorry for the delay.  Parts 1 and 2 of this article
appeared in CED digest volume 3, numbers 16 and 17.]

Pits and blisters
  One of the earliest experimental optical-digital-disc
systems was developed by Philips.  Its tellurium-coated
discs have a hermetically sealed air space.  For archival
storage, the micron-size pits must remain perfect for many
years.  But air or water vapor oxidizing tellurium after
the pits are formed creates defects.
  The 3M Co. developed an approach that avoids tellurium
altogether.  Its experimental discs have three layers:  a
high-melting-point plastic on the surface, a plastic be-
neath it that creates gas when heated, and a reflective
surface on the bottom.  A laser heating the middle layer
causes a bubble to form on the outer surface.  To read the
disc, a laser beam shines through the bubble and is reflec-
ted from the bottom layer.
  Proponents of 3M's technique claim a "cleaner" signal
with the neat bubbles during playback; pits burned in metal
have jagged edges that produce signal noise with stray re-
flections, they say.  But an RCA researcher cites the frail-
ty of the bubbles as one of the reasons his firm abandaned
the bubble approach.
  Drexler Technology's Drexon discs have minute silver
halide spheres and filaments distributed in a plastic, making
it reflective.  These metal particles absorb laser light
during the "write" process, and have lower reflectivity (like
pits in thin-metal discs) during playback.

Electronic offices
  Although the recession may slow introductions, optical digi-
tal recorders have been under development since the 1960's,
and various systems using the hardware are finally on the way.
  Toshiba has an office system with a built-in laser printer
to produce copies of documents stored on optical discs.  The
unit also has a facsimile scanner to convert printed or type-
written material into electronic signals for disc storage.  A
Philips system, called Megadoc, has similar capabilities.
  One disadvantage of optical discs, the inability to erase
them for reuse, may not be overcome until the 1990's.  But
meanwhile, permanent-storage digital discs are expected to have
a major impact on automated office systems and on systems used
for storage of huge computer data bases.
  How about optical digital recorders for the home?  RCA's
Bartolini is skeptical.  "Playback of digital samples is more
forgiving," he said.  The technology in conventional consumer-
model disc players is adequate for playback, Bartolini ex-
plained, but the ultra-precise standards needed to record
micron-size pits are an obstacle to home machines.

[A photo accompanies the article showing two engineers holding
 up an optical disc, with the apparent reading/writing device
 in the foreground.  The caption reads "High-density optical-
 storage disc, patented by these RCA researchers, holds 100
 billion bits of information on two sides--enough for an entire
 encyclopedia."]

[Another photo shows a consumer-looking player/recorder, along
 with a cutaway drawing of the read/write mechanism and a
 cross-section of a disc showing the pits recorded on it.
 The caption reads:
     "At a ralroad station in Kyoto, Japan, a travel agency
   has been using Matsushita's still-picture video recorder
   to show travel scenes for its package tours.  The new opti-
   cal-disc recorder-playback unit (photo) can store 15,000
   frames of TV pictures.  Unlike most conventional methods of
   information storage, the disc recorder needs no processing
   time.  Connect a TV camera or another source of video sig-
   nals--say, a freeze-frame tape machine--and the disc recor-
   der can "grab" individual TV frames.  A built-in microcom-
   puter aids retrieval of frames within 0.5 second.
     Matsushita's recorder employs technology similar to that
   going into prototype optical-digital-disc machines: A solid-
   state laser "burns" a pattern representing each TV frame
   into a thin film of material on the disc.  To play back the
   recording, the same laser, operating at reduced power, beams
   light on the concentric groove used for each picture.  Re-
   flected light is then reconverted into the original TV image.
     During recording the video signal varies the intesity of
   the laser beam.  A chain of pits (diagram) with different
   reflectivities is created on a tellurium suboxide layer.  The
   beam penetrates a thin protective disc layer.  A linear motor
   and encoder position the laser for recording and playback."]
   
-- 
Neil - nw1@gte.net
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