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BELL  /  AT&T   MODELS  2500

 

T O U C H   T O N E   PHONE     Bell/WesternElectric / USA (1965)
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T H E   R E D   T E L E P H O N E                      Model 2500

The debut  of the  "RED TELEPHONE"  was in the 60/70s "Cold-War's
Hot-Line"  to the  Kremlin.  This  was  the  1st  step  into  the
"Electronic  Age":    Only  1 ( one! )  transistor  and  lots  of
mechanics  -  as  can  be  seen  in the picture  of the keyboard,
taken on a mirror ...

     Column Frequencies (Hz)    DUAL-TONE - MULTI-FREQUENCY 
       1209  1336  1477                ( DTMF )
     +-----+-----+-----+
     |     | ABC | DEF |
     |  1  |  2  |  3  | 697
     +-----+-----+-----+
     | GHI | JKL | MNO |
     |  4  |  5  |  6  | 770
     +-----+-----+-----+
     | PRS | TUV | WXY |
     |  7  |  8  |  9  | 852
     +-----+-----+-----+
     |     |OPRTR|     |
     |  *  |  0  |  #  | 941
     +-----+-----+-----+
        Row Frequencies (Hz)

Historical Remarks ...

R E M A R K   T O   R E S T O R A T I O N :
-----------------------------------------------------------------
If you got a touch tone telephone and all is working well ( bell,
communication ) except the KEYBOARD doesn't react, than TRY THIS:
The keyboard is sensitive to the polarity of the incomming wires.
Exchange the wires ( RED, GREEN ) either in the outlet or in the
telephone, or use a "crossed" cable between telephone & outlet.

I T   M A Y   B E   N O T   N E C E S S A R Y  ...
==================================================

        

T O U C H   T O N E   PHONE     AT&T/WesternElectric / USA (1982)
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T H E   B L U E   T E L E P H O N E               Model R 2500 MG

has a GRAETZ-BRIDGE  ( Part = 840364202 / 9-82 )  implemented ...

           

Known from  power units ( AC/DC-Conversion ):  Independent of the
polarity on Input-Pins 2/3, the Output 4/1 is always ( +/- ).

impressum:
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© C.HAMANN   http://public.beuth-hochschule.de/~hamann   07/09/14