Michigan Bell 551C KTU

[Babybearjs]

Found this on Ebay, $9.99 plus S/H. please verify model number.... it looks like a W.E. 551-C KTU, am I right?

[poplar1]

551C KSU (Key Service Unit) with 118A Ring Generator---You just need four 400-type KTUs

[podor]

Well bought! The ring generator alone is worth $40+ on its own. Make sure to grab KTUs that are 400c issue 15 or higher if you want to use the system with VOIP vs a regular POTS line.

[Babybearjs]

thanks for the verification. I love finding stuff like this.... once I get it, clean it up and test it.... I already have some 400 series cards that are in another System in storage.... I hope everything works... but won't know till I get it....  I'm looking for a 407 KTU... anyone have a spare for sale? Now, I'm looking for 2 of them.....

[Babybearjs]

well, I got the unit today. spent the afternoon cleaning the unit. I noticed that it has room for a "Options" socket. Did any of these ever some with a 5th Plug for a 401 KTU? this one is strictly 4 CO lines only. The original 25 pair cabling that I had to remove showed that it was originally wired for 3 CO Lines, so the 4th could have been the ICM circuit. The unit is still awaiting to be tested. I'm down with a seasonal head cold right now, weather has been changing for winter, Etc. anyway, I took some pictures of the unit after I cleaned it... so I'll post those later. from what I could conclude about the origins of the unit, it had been in a building that was torn down. and possibly in a fire... its hard to tell.... signs of soot, or just age.... or it could have just been in a dirty warehouse in storage... but, it did have a black film on it that came off easily, so it could have been anything.  this is my first W.E. 551-C and I am looking forward to playing with it later.....

[unbeldi]

I believe the C version of the 550 and 551 came out in 1976.
BSP 518-215-407 is Issue No. 1, dated July 1976.  Previous BSPs do not discuss the C version.

Like the predecessors, it has four sockets for KTU cards, and two jacks for an interrupter.

Are you saying it has an additional JACK, rather than a PLUG?


Here is the description of the intercom circuit in the BSP:

Manual Intercom
3.11 This feature is provided by installing a 401A
KTU in the KSU. In early production models
of the 550/551C KSUs, only jack J4 was factory-wired
with the talk (A) battery and ground required for
operation of the 401A. Later models (indicated by
an asterisk [*) stamped after the code on the KSU)
are wired to accept a 401A KTU in any of the
four jacks.
3.12 The early models can be modified to accept
a 401A in another jack by disconnecting the
green wires from terminals 3 (A grd) and 18 (A
bat) of J4 on the back of the KSU, and transferring
them to the same terminals of the desired jack.
3.13 On the 550/551A and B KSUs (MD), the
talk battery terminals are factory-wired at
each KTU jack, but only the BR-W/W-BR pair on
J4 is wired back to the talk battery terminals on
the connecting block. The pairs from the other
jacks are dead dressed. To use a jack other than
J4 for the manual intercom KTU, disconnect the
BR-W/W-BR pair from the back of the connecting
block, and connect the pair from the other jack
as shown in Table B. Insulate and store the
disconnected pair.

[Babybearjs]

I don't know why, but I can't post pictures to this thread right now. I have tried twice, and the system times out and drops the message. so, I'll try it later.

[Babybearjs]

I found the cards for my unit.... someone was selling a lot of 4 400D cards for $9.99 plus shipping. I grabbed them.

[Babybearjs]

well, the unit is now finished. I got the 400D cards the other day and installed them. put power to the unit and tested it... all station cards work.  checked all connections and everything is wired right.... anyone want to buy it?? $299.00 plus $50.00 S/H.