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235 KTU
#488311 10/09/11 03:59 PM
Joined: Nov 2009
Posts: 451
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Joined: Nov 2009
Posts: 451
Hi again,

I have a question about the 634DA Call Director (18 button).

I was enjoying reading the BSP section 502-610-417 (March 1974), and it made referrence to the 236 type KTU that must be used with the 30 button Call Director. There was a vague mention of a "station concentrator", and I am wondering if this 236 KTU was this device. I am completely ignorant of the "station concentrator", but I am guessing (there I go again) that it allows more stations to be accessed via the Call Director than there are physical three pairs copper wires for.

If anyone has any info on this, please let me know. A wonderful soul over on the TCI mail reflector is sending me a green call director, and I am trying to learn as much about this as possible.

Thank you in advance!


Joe Herdler

Real comms took 200lb teletypes, hand keys, sounders, operators and cranked phones!
Telephone Equipment Search
Re: 235 KTU
#488312 10/09/11 04:21 PM
Joined: Sep 2006
Posts: 3,280
Online Content
Joined: Sep 2006
Posts: 3,280
Here's what I said the last time:


Posted 30 October, 2007 17:56

A line concentrator is a piece of relay equipment that uses one common T&R, plus one control lead per button, (like an "A" lead) plus a lamp pair per button, between the set and the equipment. The control lead operates a relay that applies T&R of the associated control circuit's talk path onto the common T&R to the station, and lights the line lamp.

They were used in installations where many multi-line Call Directors or answering turrets were used in a large "square" wiring format, in order to save on copper cabling.

In the list of nightmarish repair assignments, working on a concentrator is up there near the top. Not quite as bad as a crossbar ACD (automatic call distributor.)

Mathematically, the conventional installation would use, as a best case, 2.5X pairs plus a ground, where X is the number of CO lines.

The concentrator uses 1 pair plus 1.5X pairs where X is the number of CO lines.

A 29 button Call Director would therefore use, as a minimum, 72.5 pairs plus a ground.

The same 29 lines on a concentrated tel set would require 43.5 pairs plus a ground.

You can see the how the copper savings would accrue in a large system that had sets with 100 lines or more.

The reason that lamp grounds cannot generally be concentrated is that with long runs of cable, and many lamps lit at the same time, you get a condition known as "cross-modulation" the effect of which is lit lamps will go dim or almost out when other lamps turn on. That makes lit steady lamps look like they're flashing, but in an opposite cadence to the ones that are really flashing. It makes accurate operation of the set difficult.


Arthur P. Bloom
"30 years of faithful service...15 years on hold"

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