1950's era telephone switch gear

[raptor1956]

Here's a pointer to a really nice video demonstrating the switch gear used to connect the phone to the desired number -- note the numbers were only 5-digits long back then.  I seem to remember a video on the "Secret Life Of Machines" series about this as well -- man I loved that show!




Brian

[Tony_G]

Nice. AT&T Archive is a treasure.

I did a post on the Herbert H Warrick museum here:

https://www.eevblog.com/forum/chat/the-herbert-h-warrick-jr-museum-of-communications-in-seattle-lot-of-images/msg1301187/#msg1301187






If you're in Seattle it's really worth the visit.

TonyG

[chris_leyson]

Strowger switches, a really cool invention, patent applied for in 1888 and granted in 1891. US447918.
https://patents.google.com/patent/US447918A/en
Maybe the founder of the the internet is Almon. B. Strowger because of his routing switch, the technology has changed but the underlying principles have remained the same. 

[rcbuck]

It is amazing all the changes that have happened in Telcom since I worked on these steppers in the 60's, early 70's. They made a lot of noise but worked well.

[raptor1956]

Ah yes, I found it ... here's 'The Secret Life of Machines" episode on the telephone which includes a segment on the Strowger switch.




Brian

[TerraHertz]

A friend of mine used to work in NZ rotary selector telephone exchanges. He mentioned that traditionally there was a job of 'contacts cleaner' - as you'd expect, someone who did little but go through the rotary switches cleaning contacts.

Until someone did a reliability study, and found that failure rates were lower if you just left them alone.

He's passed away, so I can't ask for more details.

[GlennSprigg]

Sniff Sniff ??....  Aahh.... I can still smell the Trichlorethelene dipped little leather pads on sticks,
while I cleaned thousands of such rotary/relay contacts about 45 years ago !!!!   
[Edit]  Just saw TerraHertz comment after posting!

Which also just reminded me when about (35-40 ?) years ago, I was involved with a HUGE construction for
an automation plant, involving about 9000 relays/timers, and 500 miles of internal building wire, over about
18 large conjoined panels. About 2 years before the advent of PLC's !! which would make it superfluous !!
ALL the many thousands of panel interconnections had both ends of all the wiring numbered/lettered with
slide-on coding, so that after testing in Adelaide, ALL the massive looms were disconnected & boxed, to be
sent to Western Australia with the Panels, for re-connecting again.   And it all worked !   
The circuitry was so complex, that each Sprecher & Schuh relay, was customized with various 'contacts', like a Lego Kit,
not only for the obvious N/O & N/C contacts, but some were often delayed, so as to make/break before others....

Sorry about rambling on !! but I don't have much left now, than to 'remember' 

[GlennSprigg]

A friend of mine used to work in NZ rotary selector telephone exchanges. He mentioned that traditionally there was a job of 'contacts cleaner' - as you'd expect, someone who did little but go through the rotary switches cleaning contacts.
Until someone did a reliability study, and found that failure rates were lower if you just left them alone.
He's passed away, so I can't ask for more details.

Hi TerraHertz....  The interesting thing, is that 'later' in my career(s), as a Tech in charge of various
automated plants/machinery, that it depended on the 'voltage' across such contacts !
Where contacts were switching say 240v in the control-circuitry, we found that this would 'burn' through
any oxidization of the contacts! (And no real load as such). HOWEVER, low voltages, say at logic level 3-5v
or even say 10-12v, did not have that ability, and so oxidization could & was at times, a problem.

[GlennSprigg]

P.S.    (sorry  )
In production lines we ('I') was always thinking about not just down-time for a Machine, but
daily production costs for a whole particular 'Line' !!  What that means is this......

If one piece of machinery is holding up a whole LINE, then keeping it running is/was imperative.
However, certain 'machinery/equipment' was not dealt with the same way...
(We) may do total 'maintenance/time' on a machine, such that the COST of such 'maintenance'
'exceeds' the cost of down-time to a degree, if/when i fails!!  In other words, sometimes, it's
better to let it 'break-down' for say an hour each month, than to overkill the maintenance !! 

[Bud]

It is amazing all the changes that have happened in Telcom since I worked on these steppers in the 60's, early 70's. They made a lot of noise but worked well.

As a kid back then i was fascinated by them. I had a few of different sizes from tiny to huge ones and could spend hours playing with them. Some actually were pretty silent, making just gentle soft sound as they stepped. Perhaps people knew at the time how to damp mechanical noise, not like today when tiny relays in your scope make loud banging sound at startup.

[soldar]

I started my working life in the early 1970s when rotary switches were being replaced by crossbar switches. For some years I worked for a company that imported and installed crossbar switching equipment.

You could tell what customers had the newer crossbar switches because the dial tone was there before you got the speaker to your ear while with rotary switches you had a to wait a second or two to get a dial tone.

[Red Squirrel]

I love those AT&T videos.    I work in a telecom CO and our office area is where the old switch was before they upgraded to DMS100 which is still running today.  We manage quite a few DMS100, 200, 10, 1U etc.   Never seen a mechanical switch operational in person myself though, I think we had a CO that still had one (was off) but think it's gone now.  Would be cool if they had kept at least one though as a conservation piece.

There are oddball parts that have stuck around though, like this:

[raptor1956]

Even before the switch gear mention before they had the switch board patch panel with human operators.  The last one in operation by AT&T was decommishioned on Santa Catalina Island California in 1978.




Brian