Stromberg-Carlson XY PBX brief demo

A quick and crude video of a vintage Stromberg-Carlson XY PBX undergoing restoration in the California high desert. (This would only be of interest to vintage-phone phreaks; don't say I didn't warn you.)

See http://www.youtube.com/watch?v=wRQWhmDxPGY for more on this system.

The shot opens next to the XY line-finders as a test set is taken off-hook. The line-finder hunts for the station line that has been taken off hook, and provides the connection from the calling extension to a matching XY connector switch. Next, a view of the line-finder allotters (rotary switchs just to the right). The allotters assign a line-finder out of the bank to service the next dial tone request. As the phone is taken off hook again, you can just barely make out the allotter (1 of 2) spinning around to assign the next line finder to be used. Around the back side, the connector (not to be confused with a washer-dryer) is seen in operation while dialing station "15". This rings the white el-cheapo phone ("Damn phone!"). Last, the XY connector switch is shown as a new call is started and the tie-line access code "8" is dialed.

The dial tone is generated by three vacuum-tubes. I think they are 50V6s; a version of the popular 6V6 but with 50 volt filaments, supplied by 48V station battery (probably used as B+ too). The rhythmic clickity-clack you hear when the phone is taken off hook is the interrupter. This is a series of cams on a motor driven shaft that operate various switches. These provide the on-off cycles for ringing voltage, and busy/reorder tones.

The XY "Compact" model was capable of supporting up to 100 stations, but subtracting stations for dial-accessed outgoing trunks. This particular one is (probably) configured for 90 stations, and maybe 8 two way tie-line trunks (2-wire E&M type I).

Currently there are only two line-finder/connector pairs operating - just barely. There is a bunch of work ahead. Fortunately we have some factory drawings, manuals, assorted spare parts and some test equipment. We were testing it with a temporary jury-rig power supply, which is why you can hear a lot of hum coming out of the test set in addition to the lovely "honker" dial tone.

Category:

Science & Technology

Tags:

• telephone
• PBX
• vintage
• step-by-step

[OldGuy0003]

Don't you have to worry about the laundry machine being next to your switch?  Excess humidity and rust?

Looks cool. How about a better video?

[psylentlarry]

It's in the Mojave desert - hard to make a room humid, let alone stay that way. I think there were some dryer lint issues due to a busted hose at one time, so there is a lot of cleaning and oiling to be done. At any rate it can't be worse than where it spent it's working life; a little block building about 1/2 mile from the Pacific Ocean.

And yes, apologies for the very crappy cell phone video. Next time we'll use a real camera. Will also see about a phone patch to pickup the line audio.

Thanks!

[joetalbot760]

New updated (and clearer) video of this switch. See how it works! Play with it yourself by dialing (805) 741-2600.

Search youtube for Stromberg Carlson XY Tour

[voxframe]

Sweet stuff!!! Called in to hear the switch tonight. :-)

[scottfree2600]

You can play with this switch in "real time" by calling +! (805) 741-2600. You'll hear the vacuum tube generated dial tone, then you can dial a 2 digit number (try 12 or 22)

and then you'll hear vibrating reed generated ringback tone or mechanically interrupted busy tone.

[kjfitzgerald593]

That is cool to see and hear this one. I got to see one in use on Beaver Island, Michigan back in 1980. I feel very lucky to have seen that one. Thanks for posting this.

[An805Guy]

Interesting, so I hope you do make another longer, and higher quality, video.