Sam Spade wrote:
> As I recall, operators had dials that did 20 pps.
I only saw one PBX switchboard with fast dials (at a large hospital),
all other cord boards I've seen had plain dials, very rarely a Touch
Pat, do you recall what kind of dials your hospital job had?
Central office operators had push button dials which were developed
around the late 1940s, though some were from the 1920s (such as manual
The transmission signal protocols from one central office to another
varied over time for both local and long distance and by office type.
I believe from the Bell System history that the switchgear for the
operator would automatically transmit the appropriate protocol from
push button dials; this was handled by the trunk circuit. These
buttons were arranged in two rows of five. Central office operators in
low use boards might have real dials.
As an aside, I understand a supplemental automation for cord boards
came out in the 1970s to extend their life. [If anyone knows more
details would you share it with us?] Cords were still used, but the
dial was replaced by a series of modern keys and digital readout and I
suspect they had automatic AMA and routing built in. I saw a photo of
a huge C.O. cord board of 1970 and it appeared most operators were
making mark-sense notations, not doing connections, and they had only
a few cord pairs at each position. Basically those operators were
more billing clerks than connectors. If the new system could handle
AMA by key recording calling and called number and the times it would
be a big saving over writing tickets. Filling in those circles is
tedious and slow; it's like taking the SATs all day long every day.
Mr Joseph Singer wrote:
> Personally, I don't believe it caused any more wear and tear on
> equipment than what a 10 pps dial would make on the system. Since
> panel, #1XB and #5XB all used common control and didn't do anything
> til the requisite amount of digits had been entered in the receiving
> registers likely could care less how fast the pulses came into the
> registers. And I don't think it caused any more wear and tear than
> receiving MF or DTMF.
That's correct for common control systems. It required only relay
operation, not moving parts.
> Wear issues weren't likely the problem with 20 pps dials o n SXS. The
> problem is that SXS systems cannot keep up with pulses as fast as 20
> pps. It might work *sometimes* but for constant reliable service 20
> pps dials would not likely have enough reliability to be used.
I'm pretty sure from the history that SxS could be sped up to
accomodate 20 pps but wear was an issue since the moving parts were
moving at a higher speed. SxS switches required periodic servicing and
adjustment; the failure to do so led to some of the service crises of
the 1970s outside of NYC.
IBM had the same speed limiting problem with its electric accounting
tab machines. They tried speeding up the machines (customers
desperately needed higher speed) but wear became a serious problem and
maintenance and downtime got too high. The real solution was
electronic computers and a completely redesigned printing using a
chain intead of typewheels or typebars. IBM's highly successful 1401
computer was actually a mechanical engineering masterpiece because of
its revolutionary high speed yet clear 1403 printer. The 1403
continued onto System/360 and S/370 machines for many years. I never
could understand why IBM's competitors would market printers with
jagged lines and uneven impressions long after the 1403 set a new
standard of high speed print quality.
> As for "why subscribers were never given 20 pps dial phones as a usual
> thing" my guess is that WECO never put that into widespread production
> so it wasn't made available as a standard dial in a standard 302 or
> 500 (whichever would have been in use at the time.) When Touch-Tone
> (DTMF) came out in '64 it was a viable option that was going to
> eventually be implemented throughout the Bell System eventually.
> Whether this is the reason or not is only my speculation.
I don't know the underlying reasons but I guess that Bell didn't want
some customers to have a high speed dial when others would not in the
same town. Actually a high speed dial would more efficiently use the
expensive common control logic of panel and crossbar and ESS without
any expense on their end. (Touch Tone required receivers and initially
they were expensive). Maybe they were afraid of more dialing errors or
wanted system-wide standardization. Maybe the fast pulses didn't
transmit well on long loops from the C.O.
As mentioned, a friend jimmied his 500 set to become a 20 pps dial, so
it appears it wasn't an issue of production. (How he did it I don't
[TELECOM Digest Editor's Note: All the switchboards I worked on always
had the fast (20) dials. And in the two instances where the board had
touchtone dialing, the operator's headset muted out the tones so the
operator did not go crazy from the bleep, bleep, boop tones all day.