The Old Private Line Newsletter, February, 1999
II. What's Been Happening Lately?
Welcome to the first private line e-mail newsletter. Thank you very much for subscribing. I'm testing this free newsletter service, so don't be surprised if there are funny line breaks and strange formatting. But that's what this short issue is for -- I want to see what things look like. Let me know what you think.
II. What's Been Happening Lately?
I've been working on a number of things: the wireless article, two history questions, and a rewrite on how a vacuum tube works. I've also been musing on the complexities of spectrum efficiency. I'll cover those first three topics below and the last one in the next issue. My time is spent cruising between articles and pages within articles like a demented technical writing PacMan. I add a paragraph here, take away a sentence there, keeping with a point until I get too frustrated or satisfied. Then I come back later and do it all over again. But to specifics.
The wireless article is going well, although wireless technology is evolving faster than I can write about it. I'm in good humor about it never-the-less, and the work on it is steady. I've even produced an animated GIF explaining frequency offsets and I plan to do more on other subjects; I think such GIFs may help explain the dull, dry subject of data formats better than any written description alone. Most of the links at the top and bottom of each page now work, so feel free to roam from page to page, understanding of course that I am months from finishing:
http://www.TelecomWriting.com/PCS/splash.htm
I've received several questions about everyone's favorite undertaker: Almon Brown Strowger, inventor of the first practical automatic exchange. People want to know more so I've done some research and revised my history series accordingly. I've enclosed the new writing in this e-mail below; find the hyperlinked and referenced version inside Telephone History Part 2 at this URL:
http://www.TelecomWriting.com/TelephoneHistory2/History2.html
I've also gotten several inquiries about telephone cord history. There's not much on the web so this week I went to Sacramento State University's excellent library. They have both the Bell Labs Record and the Bell System Technical Journal. Had quite a bit of fun in the stacks browsing the dusty tomes. I've included the new text in this e-mail below. Here's the URL to look it up on the website:
http://www.TelecomWriting.com/TelephoneHistory3/History3.html
Got an e-mail from John Wong in Australia recently. He questioned my description of vacuum tube operation in the second history article.Turns out he was completely correct. After a few friendly, helpful e-mails I revised both the text and the diagram. If you've never understood vacuum tubes before, give it a try and let me know what you think. Text below and diagram at the website:
http://www.privateline.com/TelephoneHistory2/History2.html
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1. At this time we should look at Strowger's achievement, before continuing our narrative. The automatic dial system, after all, forever changed telephony. Almon Brown Strowger (pronounced STRO-jer) was born in 1839 in Penfield, New York, just outside Rochester. Like Bell, Strowger was not a professional inventor, but a man with a keen interest in things mechanical. Swihart says he went to an excellent New York State university, served in the Civil War from 1861 to 1865, taught school in Kansas and Ohio afterwards, and wound up first in Topeka and then Kansas City as an undertaker in 1886. This unlikely profession of an inventor so inspired seems odd indeed, but the stories surrounding his motivation to invent the automatic switch are odder still.
2. The many stories suggest, none of which I can confirm, that someone was stealing Almon Strowger's business and that he sought to do something about it. Telephone operators, perhaps in league with his competitors, were routing calls to other undertakers. These operators, supposedly, gave busy signals to customers calling Strowger or even disconnected their calls. Strowger thus invented a system to replace an operator from handling local calls. In the distillation of these many stories, Stephan Lesher relates a story from Almon's time in Topeka:
"In his book, Good Connections, telephone historian Dave Park writes that Strowger grew darkly suspicious when a close friend in Topeka died and the man's family delivered the body to a rival mortician. Strowger contended that an operator at the new telephone exchange had intentionally directed the call to a competitor -- an allegation that gave rise to tales that the operator was either married to, or the daughter of, a competing undertaker."
3.Whatever the circumstances, we do know that anti-Bell System sentiment ran high at this time, that good telephone inventions commanded ready money, and that Strowger did had numerous problems with his local telephone company. Strowger was a regular complainer and one complaint stands out.
4. Swihart describes how Southwestern Bell personnel were called out to once again visit Strowger's business, to fix a dead line. The cause turned out to be a hanging sign that flapped in the breeze against exposed telephone contacts. This shorted the line. Once the sign was removed the line worked again. It may be supposed that this sort of problem was beyond a customer's ability to diagnose, that Strowger had a legitimate complaint. But on this occasion Southwestern Bell's assistant general manager, a one Herman Ritterhoff, was along with the repair crew. Strowger invited the man inside and showed him a model for an automatic switch. So Strowger was working on the problem for quite some time and was no novice to telephone theory.
5. Brooks says that, in fact, Strowger knew technology so well that he built his patent on Bell system inventions. It must be pointed out, however, that every inventor draws ideas and inspiration from previously done work. Brooks says specifically that the Connolly McTighe patent (Patent number 222, 458, dated December 9, 1879) helped Strowger, a failed dial switchboard, as well as an early automatic switch developed by Erza Gilliland. But Strowger did not build the instrument since he did not have the mechanical skills. A rather clueless jeweler was employed instead to build the first model, and much time was wasted with this man, getting him to follow instructions.
6. As with Bell, Strowger filed his patent without having perfected a working invention. Yet he described the switch in sufficient detail and with enough novel points for it to be granted Patent number 447,918, on March 10, 1891. And in a further parallel with Bell, Almon Strowger lost interest in the device once he got it built. It fell upon his brother, Walter S. Strowger, to carry development and promotion further, along with a great man, Joseph Harris, who also helped with promotion and investment money. Without Harris, soon to be the organizer and guiding force behind Automatic Electric, dial service may have taken decades longer for the Bell System to recognize and develop. Competition by A.E. forced the Bell System to play switching catch-up, something they really only accomplished in the 1940s with the introduction of crossbar. And with only a few references to interrupt, let us return to the narrative.
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1. At this point I want to turn away from the narrative to dwell upon something both marvelous and mundane: the telephone cord. Many people ask when the first spiral telephone cord was introduced. Well, that depends on how you define a cord. Many early manufacturers separated a handset's four wires into two cotton covered bundles, intertwining the housings like a braid. That's like holding two strings side by side and twisting them together. One loop around the other. Is that a spiral? If so, the date of the first telephone spiral cord will be hard to track, indeed, given the numbers of manufacturers who did it, and the fact that twisted electrical cords predated telephone cords. If, however, you ask about the conventional spiral cord or spring cord of today, well, that's another matter.
2. In the early 1950s The Bell System developed an improved neoprene jacketed telephone cord and shortly after that a plastic one. The wires inside laid parallel to each other instead of being twisted around. That reduced diameter and made them more flexible. Both, though, were flat and non-retractable. In the authoritative Dates in American Telephone
Technology, C.D. Hanscom, then historian for Bell Laboratories, stated that the Bell System made the neoprene version available in 1954 and the plastic model available in 1956. These were, the book indicated, the most significant developments in cord technology since 1926, when solderless cord tips came into use.
3. Both the Bell System Journal and The Bell Laboratories Record are strangely silent as to why and when Western Electric converted the flexible plastic cords into spirals, forming the "retractile" or spring cords we use today. That such a change went unreported is unusual indeed, and I am still tracking down how this marvelous change came about.
Many people, by the way, think that the model 500 desk set, introduced in 1949, the most well known AT&T product, came originally with spring cords. Not true. They were not put on until 1954, when decorative colors were also introduced for the 500 set.
http://www.btinternet.com/~aero/tele321.htm
(braided cord example)
[Editor's note: W.E. did comment on one aspect of spring cord design. They noted that the spirals turned clockwise in the Northern hemisphere, while turning counterclockwise in the Southern. . .Okay, okay, I'm just kidding!]
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1. Dear Tom,
Amazing collection of historical background behind ATT and telephone inventors. And the early technology and how it developed. But why did you write that the glow from a vacuum tube is from the electrons. If you have ever seen one operating, you would see it is the filament heater (and you failed to mention anything about the heat boiling off electrons.
That's what gives the thermionic valve its one-endedness). You must be confusing it with neon tubes. And there it's the electrons jumping from orbit to orbit within the neon atoms.
John Wong
2. Thanks for that e-mail and the one after. To begin with, thermions are electrons derived from a heated source. One-endedness refers to this tube's valve like properties: current flows in one direction but not the other. Like a faucet, a type of valve, allowing water to go in one direction only. While I know the text below won't make much sense without its accompanying diagram, which I also revised, check it out and see if you can follow it. Here's a crude visual aid for this e-mail:
Cathode ------ Control Grid ------- Plate
(Boils off (Carries telephone (Positive electrons) conversation) energy source)
3. The vacuum tube repeater ushered in the electronics age. The device was a true amplifier, powered by an external source, capable of boosting strength as high as needed.
4. A power source provides energy to a filament or cathode within a triode valve or vacuum tube. That's the glow you see in a tube -- the filament being heated. Thus heated the cathode gives off huge amounts of negative electrons.
5. A positively charged plate a small distance away draws the negative electrons to it, much like a negative and positive magnet attract each other. An electrical field is formed, causing electrons to leap across the gap.
6. The triode's third part is a grid or control grid, which carries in our case a weak phone conversation. It sits between the cathode and the plate, the circuit so built that the grid becomes negatively charged. As the positively charged plate collects electrons the negatively charged stream from the cathode washes over the grid, tremendously adding to the signal's strength.
Ray Strackbein of http://www.strackbein.com added the following comments later:
On your diagram of the Vacuum Tube, remove the reference to "120 volts" on the filament. Some older tubes used common filaments and cathodes, but a long time ago (certainly before 1950), someone discovered that since filament voltage was usually A.C., having a separate cathode would reduce the amount of 60-cycle hum being amplified by the tube (whether diode, triode, tetrode, or pentode). The filament voltage was usually 6.3 or 12.6 VAC that came off of the filament winding of the same power transformer that used a different winding to supply the system plate voltage to a rectifier (often a 5U4 vacuum tube) to be filtered with electrolytic capacitors to become reasonably pure DC of between about 200 to 500 VDC.
The first numbered part of a vacuum tube part number told the voltage on the filament. For example, a 5U4 had a 5-volt filament, a 6SN7, 6AL5, and a 6U8 had 6.3 volt filaments, a 12SN7, 12AX7, and 12AT7 had 12.6 volt filaments. So simply remove that 120 volt filament reference and you will
be fine.
Oh yes, I was once the Chief Engineer of a TV station that used 6 tubes in the final circuit that each took 120 Amps at 5 volts on their filaments.They ran rather warm.
Click here for the vacuum tube description, complete with graphics.
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Subscribe to the Ericsson Review! It's free, well written, and full of great telecom information. And it comes from Sweden. I recommend it highly and I look forward to getting it every quarter. Take a look at its web version at this URL:
http://www.ericsson.com/about/publications/review/
And their publication called ON is also quite nice, less technical:
http://www.ericsson.com/about/publications/onmagazine/
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I get e-mail from all over the world. Next time I'll share some of it with you. For now, here's a great note from my telephone history article guestbook:
Tom:
Can you believe my boss has me doing her kids homework because she's too cheap to keep their computer repaired? You saved me with this article -- it is absolutely fantastic.
Thanks,
Someone in Queens
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That's it for this experimental newsletter! Thank you again. See you all soon at:
Best wishes, Tom Farley
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