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From: dsi@unccvax.UUCP (DataSpan R+D)
Newsgroups: sci.electronics,talk.bizarre
Subject: Re: "Magic Eye" tubes
Message-ID: <762@unccvax.UUCP>
Date: Mon, 13-Jul-87 14:31:14 EDT
Article-I.D.: unccvax.762
Posted: Mon Jul 13 14:31:14 1987
Date-Received: Tue, 14-Jul-87 06:17:07 EDT
References: <1495@frog.UUCP>
Organization: Univ. of NC at Charlotte, Charlotte, NC
Lines: 42
Keywords: anachronism, macho
Xref: mnetor sci.electronics:951 talk.bizarre:2447

In article <1495@frog.UUCP>, john@frog.UUCP (John Woods, Software) writes:
> Does anyone (a) know where I can get a Magic Eye tube (if they are even still
> made), and (b) have information on how to use them (required voltages, etc.)?
> 
> Believe it or not, I want to use this "stab from the past" to indicate
> CPU usage on a computer -- I specifically wanted something disturbingly
> anachronistic (a meter came in second place...).
> 

     Ahhhh yes, the dreaded Magic Eye tube. My favourite is the 6E5. You
might be able to get this from Richardson Electronics in Chicago, IL;
who stocks all kinds of weird receiving and transmitting tubes in depth.

     The 6E5 uses a 6-contact socket in the same pin circle radius as
tubes like the 807.  Finding a socket for this tube will probably prove
to be very difficult.

     Pins 1 and 6 (the big pins) connect to a 6.3 v heater. Pin 2 
connects to 125 - 250 vdc through a (nominally) 1.0 megohm resistor.
This is the series "triode-plate" connection. Pin 3 is connected
through a 1.0 megohm resistor to the controlling voltage. Bypass pin
3 to ground through a suitable capacitor (0.1 mFd at 50 volts should
do fine).  Pin 4 is the accelerator plate, which connects to (directly)
the 125-250 volt supply mentioned briefly above. Pin 5 is the cathode,
which should be tied through a 68 ohm resistor (or so) to ground.

     A voltage on the control grid resistor (to pin 3) of 0.0 volts
makes the "eye" appear "open", while a negative voltage of about 7
volts should just close the eye. The display appears at the end of
the envelope.

     The maximum plate current should be about 200 microamperes, while
the accelerator current is about 3500 microamperes. Your mileage will
vary.

     There is another type of "magic eye
tube, the 6AF6GT, which has two shadows which (I think) move independently
in a linear direction. The shadows are deposited on the side of the 
envelope. This tube is much less common than the first type.

David Anthony
DataSpan, Inc