0004133373@mcimail.com (Donald E. Kimberlin) (03/27/91)
David Lesher <wb8foz@mthvax.cs.miami.edu> carries on a thread
that's been of interest to me for some decades now..that of just *who*
used *what* selective ringing methods on multiparty lines. At the
time and place of my arrival into the wonderment of "the phone
company's way," all the methods he laid out for us were
well-established. But, if you asked anyone reachable the why, who and
wherefore, any answer you got was that *theirs* was the "standard
way." (Sound like today, datacomm sports fans?)
The best I've ever been able to sort out was that Bell had
apparently developed along a line using 'divided ringing') (that is,
ringing from one wire or the other to ground) for two-party or "super-
imposed ringing" (adding polarity-sensing to the divided ringing) for
four parties on one line. And, the Bell numbering scheme identifying
these never got, to my knowledge beyond four different letters. All
these range with 20 Hertz. Meantime, non-Bell telcos seemed to adopt
W. W. Dean's frequency-selective ringing, and did so in the several
variations -- Harmonic, Decimonic or Synchromonic -- and even some
combinations of these in cases I observed, to make their basic
complement more than the four or five the basic complements listed.
(Here, I can add for David's interest that in the plant of GTE
of Florida, the basic set seemed to be the "harmonic" set, but had 54
Hertz instead of 50, as well as 20 Hertz instead of 25 ... just to
show how confusing it was. Perhaps this was an answer to the
"falsing" suspicions David has. Needless, to say, you could often
hear your ringer click or buzz when another party's frequency sailed
down the line, anyway!
GTE Florida's heritage came from having once been the Peninsular
Telephone Company of Florida, which bragged it had "the first"
Strowger-supplied automatic exchange, located in St. Petersburg. That
may have been "the first" *they* knew about. But, its frequency-
selective ringing may have started the plan in that company. And,
those Strowger switches in their oak-framed glass cases were still
ka-chunking away into the early 1960's!)
Unanswered to my satisfaction is that Bell employees many
times over the years told me that "Bell companies had 8-party service,
too," but they were always evasive about *how* 8 parties could be rung
with only 20 Hertz. And, I personally did some work replacing WECo
350/355 CDO's in rural Mississippi last year, to hear these stories
proliferated. Yet, the old CDO's there had no evidence of ever having
had anything but 20 Hertz ringing generators.
So, my question to this forum, where someone certainly knows,
is *how* did Bell accomplish 8- party ringing if they used only one
frequency? Or, is it one of those bits of lore that had some truth
someplace where perhaps Bell had acquired an Independent using
frequency-selective ringing ... and then got the story embellished
with retelling and retelling?
So far, I never met anyone who could tell me just *how* Bell
did eight-party with WECo-built appratus. (No weasel stories now,
about apparatus WECo bought, resold and installed in some places. I
know they'd do that if they had to!)larry@uunet.uu.net (Larry Lippman) (03/28/91)
In article <telecom11.241.9@eecs.nwu.edu> wb8foz@mthvax.cs.miami.edu (David Lesher) writes: > Donald and others {in email} have mentioned various types of tuned > ringers. I've never seen one that was tunable by a cap, but have no > reason to think that they do not exist. So I stand enlightened. It's been many years since I have seen a frequency-selective ringer, but the style I remember was mechanically resonant. The arm (which swings back and forth between each electromagnet pole) attached to the clapper had a weight mounted at the end near the clapper. Each of the harmonic frequencies required a different weight and a different flat spring which controlled the swing tension. There were actually two sets of frequencies that were called "harmonic" ringing. The original used the frequencies: 16-2/3, 33-1/3, 50, and 66-2/3 Hz. Since this scheme was sometimes prone to bell tapping caused by, um, harmonics :-), an alternate set of frequencies was established that was pretty close, but eliminated this problem: 30, 42, 54 and 66 Hz. This alternate set of frequencies was called synchromonic. It is interesting to note that many ringing power plants which supplied harmonic ringing used different voltages for each ringing frequency, with voltages ranging for about 90 volts RMS at 16 Hz to 170 volts RMS at 66 Hz. The reason for the higher voltages at higher frequencies was to compensate for insertion loss of the telephone cable at higher frequencies. Transformers were used not only for isolation, but to permit such voltage variations. One of the earliest methods of creating ringing voltage was not through an AC generator, but used a "pole-changer" which reversed polarity of the CO battery at the required frequency. Pole-changers were operated by motors, or by a mechanically resonant electromagnet not unlike that of an old automotive radio "vibrator". Pole-changers of necessity required a transformer for output isolation. Early AC power line operated ringing power plants for PBX use also employed pole-changers instead of the ferroresonant methods which would later become popular. > He is also correct about Bell not using tuned ringers. They prefer > grounding one side of the pair, and thus adding lots of noise ;-}. I > cannot recall if the 500 set was 'gonged' or not, but guess it must > not have been. It was clearly a licensed copy, then. Grounding one side of the line is not as bad as it may seem if the telephone set utilized a cold cathode electron tube as both a DC polarity switch and as an isolator. Using such an electron tube, the ringer was effectively removed from ground during any periods of talking. The most common cold cathode tube was the WECo 426A, which was painted black and had three wires (one to ground, one to tip or ring, and one to the ringer). For longer loops where there was a possibility of bell tapping, the WECo 425A was used; this tube had four wires (one to ground, one to tip, one to ring, and one to the ringer). The [late, great] Bell System philosophy was dead set against frequency-selective ringing. Using polarity-dependent superimposed ringing, four unique parties could be signaled. Eight-party lines used coded ringing, and could be dialed directly since there were SxS connectors arranged for automatic coded ringing selection. I have never seen automatic ringing selection for more than an eight-party line. While I have seen sixteen-party lines, they were always terminated on a DSA or toll board using a manual subscriber line circuit - so the operator originated and completed all calls. > As for that nine volt supply, I have NO idea what its function was. I > just recall Lee joking about adding thousands of battery snaps along > the bus bars. Sounds like an end-cell charger to me. While no longer common for a variety of reasons, end-cells were additional batteries that could be switched in series with a 24-cell string to boost voltage and thereby compensate for reduced voltage when the cells were discharging due to AC power failure. Since end-cells could not be floated as part of the main -48 volt battery string, they were usually charged using a separate end-cell charger. Four end-cells were typical for large battery plants (> 1,000 amperes), so nine volts is about right for an end-cell charger. End-cells were switched in and out of circuit using a special switch which actually shorted them through a low resistance during the switching action; this was necessary to prevent even the slightest circuit open while the end-cells were placed in or out of the battery feed. End-cells are no longer common for several reasons which include, but are not limited to: (1) the advent of ESS has substantially reduced -48 volt power requirements, so humongous battery plants are no longer necessary; (2) almost all major CO's today have auxiliary generators capable of supplying the entire office load, thereby minimizing the discharge time of the battery plant; and (3) many large CO's that were going ESS migrated toward smaller distributed battery plants on more than one floor, rather than one large building plant. > I also recall a similar sized 48v--> 55?v beast that provided > equalization voltage for the battery plant. Most float chargers could well supply 55 volts for equalization purposes. For "problem" cells requiring a boost charge to effect overall equalization, a portable single cell charger was often employed. The battery string was not interrupted, with the single cell charge merely being connected across the problem cell. Speaking of batteries and nostalgia, any old-timers remember liquid countercells? They contained stainless steel plates, which were immersed in a solution of potassium hydroxide, with a layer of mineral oil being used to prevent evaporation. While working for a telephone company one summer while in college, I had the "pleasure" of replacing the electrolyte in some large countercells. I somehow managed to spill some electrolyte unnoticed in my shoe, with the result a few hours later that I had a disintegrated shoe and a partially disintegrated foot (which did eventually heel, er, heal)! Unfortunately, alkalai burns often go unnoticed for a much longer time than acid or other burns. Liquid countercells were eventually replaced with silicon rectifier diode stacks that were selected for the required voltage drop. Larry Lippman @ Recognition Research Corp. "Have you hugged your cat today?" VOICE: 716/688-1231 {boulder, rutgers, watmath}!ub!kitty!larry FAX: 716/741-9635 [note: ub=acsu.buffalo.edu] uunet!/ \aerion!larry
TERRY@spcvxa.bitnet (Terry Kennedy, Operations Mgr) (03/29/91)
In article <telecom11.247.1@eecs.nwu.edu>, 0004133373@mcimail.com (Donald E. Kimberlin) writes: > So far, I never met anyone who could tell me just *how* Bell > did eight-party with WECo-built appratus. (No weasel stories now, > about apparatus WECo bought, resold and installed in some places. I > know they'd do that if they had to!) Well, BSP 501-250-300, Issue 2, January 1963 describes a system where up to four parties can be signalled using Ring Party on tip, Ring Party on ring, with + or - bias, and gives the codes for the ring-back systems to select the right party. No direct mention of eight-party ringing service is made, but there are two items of interest: "Eight party line stations in step-by-step dial areas" as well as a mention of "one-ring party" and "two-ring party", which might mean that both subscriber's instruments rang, but with distinctive ringing. Terry Kennedy Operations Manager, Academic Computing terry@spcvxa.bitnet St. Peter's College, US terry@spcvxa.spc.edu (201) 915-9381
rees@pisa.citi.umich.edu (Jim Rees) (03/29/91)
In article <telecom11.247.2@eecs.nwu.edu>, kitty!larry@uunet.uu.net (Larry Lippman) writes: > The [late, great] Bell System philosophy was dead set against > frequency-selective ringing. Using polarity-dependent superimposed > ringing, four unique parties could be signaled. Eight-party lines > used coded ringing, and could be dialed directly since there were SxS > connectors arranged for automatic coded ringing selection. I don't know what our old (Bell System) switch was before it was replaced with a 1A some time in the late '70s, but it had ringback on 491x. Different values of 'x' would give eight different coded rings plus continuous ring. I miss this feature. Our current switch doesn't even have a ringback number that I can find (I've tried all the test prefixes, and located all kinds of tones, battery, terminated-no-battery, and so on, but no ringback).
0004133373@mcimail.com (Donald E. Kimberlin) (03/29/91)
Larry Lippman, as always, brings us those bits of telephone lore that help put pieces together. In his reply <Digest v11,iss247> he explains that Bell's way to ring more than four parties was to add coded ringing to divided ringing. (I probably misled the group by not adding to remarks about using "ground" as one side of the ringing circuit -- that the "ground" was through a cold-cathode diode vacuum tube in the protector outside the house.) As to frequency-selective ringers, I came along late in the territory of an Independent that seemed to have bought its equipment from wherever there was some that week. You could go into one house and find and Automatic Electric phone; a WECo in the next, and a Stromberg in the third ... plus assorted cats and dogs from time to time. Reminiscent of that time, when WECo built a pink Princess telephone, AT&T was so proud, they ran an double-page color ad about how modern they were in <Life> magazine. One of my neighbors remarked to their chum who worked for "the phone company" how classy that looked. A few weeks later, up rolled the chum in his yellow (remember those from the non-Bell telcos, folks?) truck with ... you guessed it ... in a box and proceeded to ask where they wanted it installed (the bedroom, of course, where else?). I don't recall it ever showed up on the bill. But then, it was a different time and a different society, wasn't it? Oh, ending the story about the pink Princess phone: The nice chum from the telco said he was sorry, but he couldn't make the ringer work. This is appropos of the pretty constant remarks about mechanical tuning of riningers. The "book" probably never told people to do it, but in that place at that time, it was done a fair amount. It was probably a result of running a dial network with all that hodgepodge of hardware. As what happens with so many of our narrow views of "the business," this kid thought it was just normal. and, yes, bells hummed and tinkled a lot in that place at that time. We all just thought it was normal. And, thanks Larry, for telling me what a "pole-changer" was for. I saw old references to them, but never in a context that explained what their function was. They must have been very archiac, for by the time this kid came along, all the offices I saw had motor generators for ringing current. I guess they were more maintenance free. I can only guess pole-changers went out before WW II. Larry mentioned "AC power line operated ringing plants" in the context of U.S. PBXs. Most of the Bell and overseas telcos I ever got into used a low frequency AC ringing current (16-2/3Hz in most, which is curiously the same .83333.... of 20 Hertz as 50 Hertz is of 60 Hertz. This always made me suspect I could guess where they got their first ringing generators from. What I found uniquely different was that in my Paris apartment, it seemed the PTT rang phones with 50 Hertz. This could easily have been a current-limited sample of the AC power line. I often thought that probably saved French-technology PTTS a few million in ringing generators over the years. Makes me wonder why the rest of us even bothered to get into 20 Hertz in the first place. But when Larry said: > Sounds like an end-cell charger to me..... and then: > remember liquid countercells? He brought up a whole tale I'll put into another nostalgia post, because this one is getting too long and wandering off its title. Anyhow, thanks and congratulations, Larry! I hope people like Al Varney have more to add to the "mysteries of ringing" and putting the two major ways into context.