I'm looking for #5XB training manuals [telecom]

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It certainly helped, but it was not essential for DDD. Many cities in Texas and Oklahoma, including Dallas, Oklahoma City, Fort Worth and Tulsa converted majority step-by-step exchanges to DDD with LAMA. My first DDD call, when they turned it up for employees a week or two early in Oklahoma City, was to Bell Canada in Montreal.

Wes Leatherock snipped-for-privacy@yahoo.com snipped-for-privacy@aol.com

[This is] from a Bell textbook c1979:

--No. 5 xbar originally developed for suburban residential and small cities not requiring multi-office complexities of Panel and No. 1 xbar. Many calls would be within the office. (Recall that panel and

1xbar were to solve the "big city problem" of multiple offices.)

--to be compatible with DDD and AMA (store all needed digits).

Later features over 30 years:

--Central AMA making No 5 a small toll office.

--Line Link pulsing for inward dialing to PBXs.

--International IDDD

--Centrex, including station controlled transfer.

--large auto call distributor.

***** Moderator's Note *****

Does anyone know when the last #5XB was retired, and where it was located? Are there any still in service outside museums?

Bill Horne Moderator

Per the 1925-1975 Bell Labs history:

[1982] While electronic switching systems are being introduced around the world, new crossbar systems patterned after No. 5 crossbar are still being sold in significant numbers. The last W/E built No. 5 crossbar was for Birmingham, Alabama in early 1976. More than 2,700 enttiies were provided by Western Electric, 688 of the flat spring variety. A peak of 28.5 million customer lines was reached in October 1978.

(At the same time, October 1978, peak deployment of community dial offices (small village step-by-step exchanges) was reached at 4.8 million lines. Overall step-by-step deployment peaked at 24.4 million lines in 1973).

• * *

In the late 1980s I sought to visit central offices still having electro-mechanical equipment to get photographs before it was retired. I discovered, at least in my region, everything was ESS. The Baby Bells were converting to ESS as fast as possible, including converting analog ESS to newer digital models. I also checked with small Independent telephone companies and found that they had converted to ESS earlier because ESS reduced service visits to unattended small offices and allowed introduction of profitable new services. Some offices were converted to ESS due to community growth and there was no physical room in the building to house a larger electro-mechanical switch.

I dare say some of the new or expanded No. 5 crossbar hardware installed in the 1970s had a relatively short service life, especially for telephone equipment. I don't know when the last normal full service electro-mechanical exchange (of any type) was retired, but my guess is the US was wholly ESS by 1990 or earlier. Whether the last exchange was crossbar or step-by-step I don't know.

I have no idea of the situation in foreign telephone companies where electro-mechanical may have hung on a while longer.

The Annual Reports of the Baby Bells may contain more information on their plant upgrades.

.

Northeastern Ohio or Northwestern Pennsylvania, I think. I vaguely remember a discussion of it here, including the reasons why -- though I don't remember the reasons themselvefs...