tube CD player (was Re: sizes (was Re: vacuum tube computer))

From: Gary Oliver <go_at_ao.com>
Date: Mon Feb 1 19:19:22 1999

I believe I recall a demonstration on tv in the mid 60s (1964 or so) that
showed a television signal being sent over a light beam. The receiver
was possibly a silicon "solar" cell. I think selenium MIGHT be fast
enough, but a photoresistive cell like CdS would be way too slow.
I remember trying to use a CdS cell to do a "talk over a light beam"
experiment as a kid. Barely worked. Changed to a silicon cell that
came out of a 1950s photometer and it worked great. Granted it was
about 2cm X 4cm - a bit larger than optimal for the beam sensor on a CD.

I don't believe a silicon device would be entirely anachronistic - even
my 1940-something flexowriter has silicon diodes in it. Big hurky
cartridge diodes, but silicon, none-the-less - at least that's what
they appear to be from their electrical characteristics.

Gary

At 12:41 AM 2/2/99 +0000, you wrote:
>On Feb 1, 23:30, Eric Smith wrote:
>
>> Of course. It would use a HeNe laser, just like the early laser video
>> disc players.
>>
>> The part I haven't figured out is the photodetector. Even those early LD
>> players used a phototransistor for the detector.
>
>Would a selenium cell be fast enough? A CdS photresistor probably wouldn't
>be, I think.
>
>--
>
>Pete Peter Turnbull
> Dept. of Computer Science
> University of York
Received on Mon Feb 01 1999 - 19:19:22 GMT