CMS:Number Five Crossbar Switch

Number Five Crossbar Switch

The Number Five Crossbar Switch (5XB) is from the Adams-2 exchange on Mercer Island. Its configuration in the museum is around one fourth of its original size. It is one of two known 5XB's to exist in the present day.

In Active Service

The Adams No. 5 Crossbar was installed on Mercer Island in a newly-constructed building in 1957. The installation force was about 50 Western Electric employees, and the switching hardware itself cost an estimated $554,000 (1958) or $6,181,000 in 2025.

The switch was cut over on Sunday, February 9 1958 just a month before 2L-5N dialing was introduced in the greater Seattle area. It relieved the Parkway exchange of the Mercer Island traffic that was previously handled there via underwater cable. Along with the cutover of the machine, switchman Don Fagerholm, a long-time resident of Mercer Island, transferred from the Parkway central office, to the new Adams office on the island. He stayed with the switch for much of its life, including its retirement. He was still on staff at Adams after the 5XB was replaced by a 1ESS in the 1980s.

Museum Life

The Telephone Pioneers selected this exchange as a likely candidate for the museum, and after permission was given to transfer it to Duwamish, Don Fagerholm selected the frames to take, and supervised the early installation of the switch in the museum. Volunteer Bob Dickensheets also had a very significant role in installing and maintaining the switch at the museum

In addition to equipment from Mercer Island, the museum's 5XB also has frames gathered from other offices as well, including:

• Completing marker 1 (CM1), a U & Y type marker that is an older design than the wirespring CM0
• A "minibar" auxiliary line link frame with mini crossbar switches
• An older style number group from the RE-2 office
• LAMA frames from an unknown office.
• Revertive pulse outgoing senders (OS's) and incoming registers (IR's) from New York.

Since its basic initial installation, the 5XB has been expanded and augmented by museum volunteers in order to present a more complete view of the capabilities of the machine. In the 1990s, Steph Kerman donated the RP OS's and IR's mentioned above, allowing the switch to once again communicate with the museum's panel office. The OS's feature a novel modernized counting chain circuit on a printed circuit board, manufactured by CMC Corporation to replace the 208 type relays and RP stepper that would have previously been used.

In the late 2010's volunteer æstrid Smith wired up the Pretranslator (PRT) to allow the machine to translate on a varying number of dialed digits. (Before this was returned to service, a museum caller could not dial common three digit codes, like 411, 511, etc. They had to dial a full 7 digits, like 511-1111 in order to complete their call). At the same time, æstrid and Sarah Autumn configured the machine to place calls to the C*NET collector network via kercheep using 1+7D dialing.

In 2021, volunteer Sarah Autumn fully repaired the trouble recorder, which had not been working for several years. This was a substantial addition to the switch, as the trouble recorder was one of the primary diagnostic tools used by technicians.

In 2022, Sarah brought up the ANI frames, which allow the 5XB to outpulse the calling number to the kercheep tandem. For example, dialing KE7-1111 from the 5XB will cause kercheep to read back the phone number of the calling telephone which is sent out from the 5XB during the call setup process.

In 2022-2023, Sarah acquired further equipment from Steph Kerman and Steve Flocke which allowed the switch to complete coin calls, both on an Intraoffice (IAO) and inter-office basis. Steve Flocke's main contribution was the Coin Supervisory Link, which he designed and built for the museum.

In 2024 Sarah wired up the Automatic Monitor Register Sender Test (AMRST) equipment in the Master Test Center (MTC). This equipment allows the 5XB to monitor and test its own senders and registers for faults while in operation.

Technical Details

Maintenance Aisle

• Trouble Recorder
• Master Test Frame (MTF)
• Automatic Monitor Register Sender Test (AMRST)
• OGT jack panel and OGT test frame
• AMRST relay bays
• MTC connector bays
• Miscellaneous relay rack with MDT, supervision test, and alarm circuits

Marker Aisle

• Foreign Area Translator (FAT)
• Completing Marker 0 (CM0)
• Completing Marker 1 (CM1)
• Auxiliary Line Link (ALL) (not in use)
• Route Relay Bay
• Dial Tone Marker (DTM)
• Number Group Connector (NGC)
• Number Group 0
• Number Group 1 (not in use)
• LAMA Transverter & Billing Indexer
• Master Timer

Register and Sender Aisle

• Power Ringing and Tone Distributing frame (PRTD)
• Pretranslator frame (PRT)
• Outgoing Sender Connector (OSC)
• Originating Registers (ORs)
• Originating Register Line Memory (ORLM)
• DTMF decoders
• Outgoing Senders (MF, DP, RP)
• Coin Supervisory Link (CSL) and Coin Supervisory circuits
• Service Observing circuits
• Incoming Registers (MF, DP, RP)
• ANI Transverter (ANI TV)
• ANI Transverter Connector (ATVC)
• Outgoing Sender Link (OSL)
• Dimond Ring Translators 0 & 1
• Incoming Register Links (MF, DP) (IRL)
• Automatic Progression Trunk Test (APTT)

Line Link Aisle

• Line Link Connector (LLC)
• Line Link Marker Connector (LLMC)
• Line Link frame (LL)
• Trunk Link Connector (TLC)
• Trunk Link frame (TL)
• Miscellaneous relay racks
  • IAO trunks
  • Incoming trunks
  • Outgoing trunks
  • Coin trunks
  • Announcement trunks
  • Permanent signal trunks
  • Combination tone trunks