TELECOM Digest OnLine - Sorted: Bell 607 Dial PBX Cord Switchboard

Bell 607 Dial PBX Cord Switchboard
18 Jul 2006 14:10:07 -0700

Recently I mentioned the Bell 608 PBX, which was the last cord
switchboard developed by the Bell System and had a modernized
appearance and some automated functions.

I've discovered there was a predecessor, the 607 PBX. This looked
like a traditional switchboard (black and wood), cords, and lever
keys, however, this had similar automated functions such as automatic
ringing and flashing supervisory signals. I don't know if the 607 had
wink flash for ringing.

Would anyone have had any experience with this particular board? I
suspect it came out in the mid 1950s. I'm not sure how it related to
the 555/556; they had modular components but no automated features.

For those unfamiliar with switchboards (cord or cordless), they
contain "supervisory signals" which is the status of whether the
telephones are on hook or off hook. These tell the operator whether
the call has been answered or whether the call has been completed.

On cord switchboards, these were small lights at the base of the
cords. On meant on-hook, off meant off hook.

On busy boards the operator had to remember, for each cord pair,
whether the call had been answered or completed. Either would display
on-hook. For not answered, she'd have to continue ringing or get on
and take a message. For already done, she would disconnect.

The 607 and 608 boards provided automatic flashing of supervisory
signals to aid. A slow wink indicated ringing, a fast wink indicated
a user flash for operator. These help productivity.

What is sad that today PBX operators have no idea about these things.
They connect you and forget about you. If the called party is busy or
doesn't answer you're out of luck. Sometimes you'll come back to the
board as a fresh call and the operator will just plug you in all over
again, not realizing the called party isn't answering and you need to
be referred to someone else or a message taken.

[TELECOM Digest Editor's Note: The 607 came out in 1950, and that was
what we had at University of Chicago (actually a 26-position, broken
in two groups of 12 positions and one group of 2-positions) when I
worked there in 1958-62. In addition to what you noted above, each
position had a 'tie-line' plug on the bottom row of plugs to every
other position; the tie-line plugs were in a sort of 'rotary hunt'
arrangment; unlike the other lines where we had to 'test for busy'
before plugging in and ringing ('test for busy' meant touch the tip of
your cord to the sleeve of the plug on the board; if you heard a
'crackle' sound of static in your ear the line was free and you could
use it; if you did _not_ hear the 'static noise' it meant [and your
report to the caller was] 'line is busy') with those tie lines you
just plugged in, waited for another operator to answer then passed the
desired extension number. The reason you had to do this test was
because some other operator down the line who multipled to that
extension might have a cord up down there. If you did not test for
busy first, you might well accidentally put an unwanted 'three way
call' up in error.

The three clusters of positions were known informally as 'Midway' (for
MIDway-3-0800 the main campus number with 59 incoming lines in rotary
hunt; PBX extensions were numbered in the 2000-4999 series), 'Museum'
(for MUseum-4-6100 which was the main number for the hospital/medical
center complex with 93 incoming lines in rotary hunt; PBX extensions
were numbered in the 5000-6999 series plus Telepage '7') and 'Normal'
(for NORmal-7-4700 which was the Fermi Computation Center main number
with about 20 incoming lines in rotary hunt; PBX extensions numbered
in the 8000 series). The extensions could all dial each other of
course, but incoming calls from outside were _supposed_ to begin with
the outside caller using the 'proper' listed number to reach us. But
many folks would call the medical center (MUseum-4-6100) and then ask
for the 'personnell department' [for example] which was part of the
main campus MIDway-3-0800, so whenever an incoming caller wound up on
'the wrong board' the operator had to transfer them via the tie-line to
the board on the other side of the room; sort of like the old 'A' and
'B' board arrangement. And yes, it was otherwise a 607 board in terms
of automatic ringing/flashing-back/ etc.

When the 607-style boards were first installed -- they told me it was
about 1949-50 -- all five thousand plus extensions (main campus,
hospital and the (then new) Computation Center were assigned to
MIDway-3-0800; there were then a couple hundred lines in rotary hunt
used, I think from 0800 through 0999, but the 'powers that be' decided
the traffic congestion was just too much, and it had to be split up
differently. All the student dormitories, faculty housing and the
'International House' (sort of a 'YMCA-like' place on campus) all had
their own switchboards as well, all of which had extensions from our
main board _plus_ their own 'outside' 7-digit numbers to use as their
incoming/outgoing lines. For about six months, they had me work over
in the medical center at the 'psychiatric board' (that is, the switch-
board in the psychiatric unit at the university hospitals). There were
five or six extensions from the main phone room and each of the psych
doctors had their own private extensions as well.

I think about 1963-64 Illinois Bell decided the entire mess should be
done over; they got University of Chicago to split the cost with them
fifty/fifty to install centrex; over on 61st Street and Kenwood Avenue
(across the alley from 'Kenwood Bell' [the central office for the
whole area] Illinois Bell built an area for a new centrex
installation. It was down the street from the university power
plant. It took them about a year to construct the whole thing, and
they put it on the 312-753 exchange. PAT]

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