[GreenKeys] ASR33 modem

[B M]

Many thanks to Chris, Nico, Jim, Richard, Randy, and Wayne  (I
appologize if I missed anyone!) for the information.  This list has
been fantastic in supplying information.

Remaining problems:

1. It appears my mode switch is operating backwards.  With the modem
disconnected and nothing is connected to the send/receive lines, the
TTY runs open when in 'Local' mode, but is locally operable in 'Line'
mode.  I will investigate the wiring on the actual switch.  I suspect
it is backwards from the label on the cover.

2. The Paper tape reader does not seem to work.  The fuse on the
183087 board keeps blowing.  I only had 1/4 watt fuses, but the board
does require 1/2 watt fuses.  I will get the proper wattage next time
I am in the city.  I checked all of the resistors and they appear to
be within tolerance.  Is there any way of checking the capacitors
using a multimeter?  I do not have a capacitance checker. The tape
reader is the manual version.  When I flip the switch to read, the TTY
appears to run open (lots of noise, nothing printed) and the tape does
not advance.  The tape out switch appears to be working.  Any ideas?

Question:

1. The TTY I have has a fake wood tabletop which sits on a salmon
colored base.  The tabletop appears to be professionally built since
all of the router work is very clean and exactly matches the
dimensions of the TTY.  Is this an option from Teletype, or is this
base from another company?

Here is a summary of what I have found to date.

The internal modem is connected to the TTY via the Molex connector P2.
 Disconnecting P2 disconnects the modem.  I have only been able to
locate the patent for the modem, but no documentation on it.  If
anyone has documentation, I would sure appreciate it.  There are
several ICs on the modem and they appear to be made by ITT with a date
code of 6903.  There are several other components that look like
transistors, but they are not in the usual metal can nor plastic
variety.

Does anyone know where the molex plugs can be ordered that fit into
the connectors on the TTY?  I would like to make a permanent cable
that can be plugged in.

 P2:       (Note pin orientation between the plug and socket!  The
orientation is a mirror image of each other.  Pin 1 is the lower right
when looking at the P2 socket)
    pin 5 -Send
    pin 6 +Send
    pin 7 -Receive
    pin 8 +Receive

Terminal Strip:
   3 -Send
   4 +Send
   6 -Receive
   7 +Receive

Be very careful with pin 1 and 2 of the terminal strip!  I
accidentally found out that these pins have live AC on them!!  (I have
to get a new screwdriver and I did find that the circuit breaker is
operative).  Note to self: always unplug device from power when
messing with the innards :-)

The modem will find the carrier in both Local and Line modes (I used
Audacity, an open source software program to generate the answer
carrier frequency of 2125 Hz).  The carrier light should light up when
the answer carrier frequency is detected.  Note that the microphone on
the acoustic coupler is very sensitive.  I generated the carrier on my
laptop which was sitting about 3 feet away from the TTY and the TTY
detected it!  When in 'Line' mode, random characters will be printed
when the carrier is detected.  This is presumably due to the ambient
noise when the handset is not in the cups.

For those who are interested, I acquired the TTY for use with my 2
PDP-11 computers.  The newer of the systems is a PDP-11/10, circa
1972.  The older machine is a PDP-11/20 which was the first PDP-11
produced.  My PDP-11/20 (September 1970) is old enough that it does
not have the model number on the blinkenlight console.  Both machines
use core memory (each has 32 kWords of core) and RK05 disk drives.  I
have the PDP-11/10 in a runnable state and can boot RT-11 v2 with
MUBASIC from the RK05 disk.  Eventually, I will be getting the
PDP-11/20 running, but I need to check out the power supplies and
clean it up before I attempt to power it up.

--barrym

On Wed, Aug 4, 2010 at 3:11 PM, B M <iamvirtual at gmail.com> wrote:
> On my ASR-33, an Anderson-Jacobson acoustic coupled modem (ADT-233) is
> installed.  Does anyone have information on this modem?  I have
> googled around, but have only come across the patent for the device,
> but no further information.
>
> I am looking to connect the TTY up to my ancient PDP-11 computer, but
> I need to be sure the modem is sufficiently disconnected for the
> direct connection.
>
> Thanks!
>
> --barrym
>