atcomsystems.ca/forum Forums Other TDM Phone Systems 1A2 and Comkey Telephones & Systems curious about 1A2

EV, You are correct about those ring tranfer switches causing diode matrix ringing nightmares . If not properly installed key phones that did not share the same key lines but had a transfer switch connected to the bell in thier phone would cause the bell to ring but no key lines would light up and flash . One of the early causes of phantom ringing on key sets . Also why did some companys take the hundred pair cable on the 1a2 call commander phones and break them out into 5 amphenol connectors ? There must of been a reason !

OBTW:

Early large key sets, such as call directors, had these "five-finger" 100 pair cables that were used to actually plug directly into the key strips in the phone. The line cord was just a male to female five-finger cable. I guess this was an effort to reduce manufacturing expense and complexity.

Twisted:

I almost forgot, yes a diode matrix could be done using a standard 66 block, but Western Electric made a special block for this purpose. It consisted of five vertical rows of clips and five horizontal rows. I diode was then punched down at the desired cross points to activate the ringing for that line. These blocks could be daisy-chained to accommodate any number of lines and stations.

twisted... we did them on bix

100 pair cable for the call directors & 30 ,60 ,90 & 120 line bucket ,s wired up like 5 6 button phones & had plenty of spares, lota fun looking for a bad diode out of 100 line console not ringing or dinging

Telemarv:
That supprises me that you did them on BIX. The reason I say that; because I have been in lots of phone rooms that had the remnants of 1A1 & 1A2 and there's always walls of 66 blocks. I didn't realize we were using BIX here in the great white north that long.

Ed:
They made a category for 1A2 with you as the moderator :rofl: Sucks to be you!!

Next trivia question; where did the A1 control lead term come from? Or for that matter, 1A1, 1A2? I assume that LG came from "lamp ground?"

Simon:

The A lead is just a ground that is switched by the hookswitch and hold button inside the set. I guess they just needed two terms for either end of what is effectively a loop.

1A1 and 1A2, or GTE's 10A2 were just nomenclature for the family of hardware, just like 5ESS. 1A1 was the first generation of modular key systems made by Western Electric and when a major change came about (plug-in cards instead of hard wired KTU's(relay units)), it became 1A2. 5ESS is simply the fifth generation of AT&T's electronic switching system, the first one obviously being 1. By the way, there are still plenty of #1ESS switches in use (actually 1A's) and 4's in North America.

Oh, and yes, LG is Lamp Ground. Ding ding ding, tell him what he won, Johnny!

We had modified Logic 20s with non locking keys and a 20 button addon and the set was called a logic 40 that would work on a 50 pair cable almost 40 lines and you could add to each 40 button set another 20 button module. There was a limit how many you could put on. There was only one talk pair for all the lines and 1 A lead and 1 lamp lead for each line and the grounds were commoned up. It was sort of a concentrator It saved a lot on cabling.

Okay, kids, get to your seats and open your books to page 7. This class is entitled "Telecomm 101".

Three pair per line

Pair 1 --- Tip and Ring --- Talk Path.
Pair 2 --- A and A1 --- Battery and ground to operate relays (Hold, etc.)
Pair 3 --- Lamp and Lamp Ground ---- Lights!

Just Bill can tell you about the Central Office Toll / inter-office circuits ---- relays IDed by letters. The "A" refers to the action it controls by the "A" relay. "E&M" circuits (EAR & MOUTH) sent and received battery and ground to control the particular operation. Just like ground start trunking.

Next week we will cover "Wink" and how it starts (play on words, wouldn't you say?) :read:

Have a nice recess, class dismissed.


KLD

Thanks a lot guys for the lessons on the old 1A stuff. I never did much work with them but did replace many of them with EKT's I have an older friend that still has tons of this stuff in his now closed shop. He repaired AT&T systems for decades and taught me all I know about the 1A2 and Merlins