Telephone Switching > Cross Bar Switching

755A Trunk/Local Lights

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ESalter:
Hi Everyone-

Sorry I haven't been around for a while, I'll try to make an effort to stay a little more frequent on here.

Last week we finally picked up a WE 466 to go with our 755A.  Until this point all we had hooked up to it was a converted 460 and several various types of single line phones.  Now that we have a 466, I'm a bit confused.  The phone has lamps for all 4 trunk buttons as well as the intercom button.  There's a wire for it in the cord and the BSP for the phone shows it going back to a terminal on the PBX called "L1 (LOC)".  I can't for the life of me find any such terminal on the PBX.  My dad has a document written by another collector(I forget who) that mentions two disadvantages of a 755A are the hold feature doesn't work on intercom calls and there is no illumination on the intercom button.  I find that very hard to believe because the lamp is present, there's a wire for it in the cord, and it gives a terminal name on the schematic for the phone.  Also, imagine there is an incoming call from another station, so your phone rings.  If the intercom button doesn't flash, how do you know what button to depress to answer the call?  Assume it's a local call because none of the trunk lamps are flashing? 

So, does anyone know for sure if the 755A does/doesn't have local lamp outputs for the stations, and if so, where do I find them?

Thanks!
---Eric

ESalter:
So after quite a bit of searching I've discovered a couple things about this.  Apparently the 755A doesn't come equipped with local lamp outputs.  I found a BSP that says that functionality can be added with the addition of a relay and some wiring changes.  The set of schematics we got with the 755 does show a LL relay that operates "line lamps" which appear to be what I'm after. 

It looks like the solution is going to be to make a strip of relays to add to the PBX and make the necessary wiring changes to make them operate as intended.  My dad and I are going to try to clip-lead this up for one station to make sure it works, then go from there.  Not the solution I was hoping to find, but we'll manage.  I'll try to post photos and details of our progress just in case anyone is interested.

---Eric

AE_Collector:
Hi Eric:

I am not familiar with the 755 PBX specifically and initially wondered what the purpose of the key set was. On most of the PBX's that I worked on in the old days all trunks came to the PBX operators who forwarded the calls to the PBX stations which were mainly single line phones. We did occasionally have key sets/systems behind PBX stations for certain departments but in most cases the line keys had PBX Stations on them, not trunks.

What you are setting up would presumably be for a department within a larger company that effectively has Direct in Dial since they have key sets with direct CO lines on them and then the 5th line key has a PBX station on it. So the PBX is really just a big intercom system though this set up would also give the ability for a customer to call the main published number for the company rather than the departments specific direct numbers and then the PBX operator would put the call through to the department on the intercom/PBX station.

I am thinking that the PBX was somewhat designed around this method of operation since a 466 doesn't sound (to me) like a normal 400 series key set, maybe it is a custom key set to work behind this PBX? Presumably 1A1 or 1A2 key equipment is needed for the CO lines to operate on the first 4 line buttons. If so there is no reason that the PBX station on line 5 key couldn't also be run through a key system line circuit as well which would then provide Hold and Lamp functions as well.

If the PBX has an option to operate a line lamp for any of its stations this would potentially be an equipment cost saving over needing to use a full key system circuit but a key system line circuit fir the PBX station would likely give better functionality.

Just thinking out loud trying to picture this sort of arrangement as I rarely ever  saw this set up with PBX's here in the old days. Of course once PBX's became electronic with proprietary multi line phones available many different arrangements became much more commonplace.

How many stations can a 755 PBX support? What us the station numbering?

Do you know if all stations can operate separate line lamps if the PBX is optioned for it?

Terry

poplar1:

--- Quote from: AE_Collector on August 22, 2016, 01:58:10 PM ---

I am thinking that the PBX was somewhat designed around this method of operation since a 466 doesn't sound (to me) like a normal 400 series key set, maybe it is a custom key set to work behind this PBX? Presumably 1A1 or 1A2 key equipment is needed for the CO lines to operate on the first 4 line buttons. If so there is no reason that the PBX station on line 5 key couldn't also be run through a key system line circuit as well which would then provide Hold and Lamp functions as well.

Just thinking out loud trying to picture this sort of arrangement as I rarely ever  saw this set up with PBX's here in the old days. Of course once PBX's became electronic with proprietary multi line phones available many different arrangements became much more commonplace.


Terry

--- End quote ---

Terry. both the 750 and 755 PBXs use multi-line phones that have a common talk path for all lines. They don't have all the lines extended as pairs to each phone. The 205 telephone set used with the 750 has only 4 pairs: 2 pairs between the phone and the subset for the talk path (same as a 202), and 2 pairs for telling the equipment which line to pick up: 1, 2, 3 and a common ground. (Intercom is accessed when none of the 1, 2, 3 line leads is grounded). 755 is similar but I think also has a lead for intercom, also has 4 trunks instead of 3 (though a 4th trunk can be added to a 750A, if I recall correctly). So a key system (1A, 1A1 or 1A2) is not needed with phones on a 750 or 755 PBX, since the holding, intercom path, lamps (separately mounted in the case of 205 sets), etc. are accomplished in the PBX.

ESalter:
That's exactly right.  The 755 has 4 trunks and 20 stations.  Picture it being like a key system except the intercom/local link is private.  On key systems anyone that depresses the intercom button is connected to that link.  On a 755 those links are direct and private(it dose support conferencing though).  It's capable of 3 local links at once.  The stations are numbered 20-30.  The key sets do have a separate lead coming back to select local/intercom.   I'll try to take a video demonstrating how it works tomorrow.

---Eric

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