If I wanted to add 565/2565 speakerphone support

[David Griffith]

If I wanted to add 565/2565 speakerphone support, how would I go about it?  I can see what signals go where in the 2565 service manual, but I'm having trouble making sense of it and I don't know where to look in the Key Systems Maintenance Manual.

[erco]

On Saturday, March 9, 2024 at 11:54:48 PM UTC-8 frot...@gmail.com wrote:

If I wanted to add 565/2565 speakerphone support, how would I go about it?  I can see what signals go where in the 2565 service manual, but I'm having trouble making sense of it and I don't know where to look in the Key Systems Maintenance Manual.

Have a look at 512-700-100, the section is entitled "4A SPEAKERPHONE COMPONENTS", "IDENTIFICATION, INSTALLATION, OPERATION AND MAINTENANCE", which will be in the VOLUME 1 section of the KSSM.

That section covers the details, and includes a full wiring diagram of the 82B block and all the components and their signal names. I've taken that diagram and modified it a bit for my version of the 82B block.

The 82B block is the easiest way to put together a 4A system with a 565/2565; it's generally "plug and play". The only rewiring in the phone you might have to do is to undo someone who may have changed the default configuration by sparing off the violet pairs (such as for bridging several 2565 phones together). I cover that little detail as well as some others in this youtube video showing how to wire up a 4A speakerphone using my 82B block, which is similar to the original Bell System block, but uses jumpers instead of that strange little "partial amphenol" option block.

 

[erco]

On Sunday, March 10, 2024 at 12:07:36 AM UTC-8 erco wrote:

On Saturday, March 9, 2024 at 11:54:48 PM UTC-8 frot...@gmail.com wrote:

If I wanted to add 565/2565 speakerphone support, how would I go about it?  I can see what signals go where in the 2565 service manual, but I'm having trouble making sense of it and I don't know where to look in the Key Systems Maintenance Manual.

[..]

The 82B block is the easiest way to put together a 4A system with a 565/2565; it's generally "plug and play". [..]

I should add: the "other way" to wire up a 4A speakerphone (a way I don't know much about BTW), is by using a 223 adapter, also shown in the BSP cited above (512-700-100). But that's a bit intrusive, and involves wiring a separate (second) wire into the phone, and is a bit more involved. I wouldn't recommend that route for a 2565; the 82B block is a better way to go; cleaner, simpler.

I think the 223 block approach might be required with certain phone sets. I don't know much about the 223 block arrangement; folks on the facebook 1A1/1A2 group or sundance groups would know more about that.

If you need an 82B block, you can sometimes find them on ebay. Or if you have no other choice, you can contact me about using mine, which is just the board without any kind of enclosure, but you can find an enclosure yourself; just be sure to provide the appropriate slots for cable ingress/egress. I have use one of my 82B boards here in my office for my 4A speakerphone system, and have it mounted to a plywood backboard along with the KSU and other telecom equipment.

[erco]

Somehow this thread fell into private emails, but in one of those private emails you did raise an interesting question:

> [..] I'm curious about is how much of the speakerphone functionality relies on something in the KSU.  [..]

This made me curious too; so I wired up the 4A speakerphone to one of my Seriss KSU's (just like in the video), and then pulled power to the KSU while keeping the speakerphone power plugged in.

The speakerphone operated normally; it was able to pick up whatever line was selected on the phone, and could make calls/hang up just fine. I could also pickup the handset in the middle of a speakerphone call, and it transferred to the handset fine. And I could switch back to speakerphone by holding down the ON button on the transmitter as I hung the handset back up.

The only things that didn't work with the KSU powered off was non-speakerphone related; no line lamps, no hold ability, and regenerated ringing was out because the ring generator and interrupter were both off (provided by the KSU).

So the speakerphone really is just relying on the switches inside the phone (hook switch, line buttons, etc) to handle taking over the voice circuit, and doesn't involve the KSU's power or features at all.

[David Griffith]

Looking at your copy of the 2565 manual, I see there are several signals in the purple group of lines that seem to be for indicators and signalling regarding speakerphone functionality.  Please tell me if I have this right: it's through that group that the phone interfaces with the speakerphone stuff by way of an 82B, and that a KSU from back-in-the-day would never actually touch those lines.

[erco]

On Wednesday, March 13, 2024 at 12:02:03 AM UTC-7 frot...@gmail.com wrote:

Looking at your copy of the 2565 manual, I see there are several signals in the purple group of lines that seem to be for indicators and signalling regarding speakerphone functionality.  Please tell me if I have this right: it's through that group that the phone interfaces with the speakerphone stuff by way of an 82B, and that a KSU from back-in-the-day would never actually touch those lines.

Yep, that's all correct!

Well, for 2565 sets anyways.. and any other sets that specifically support speakerphone features over the violet pairs.

Just to be clear, there are other phone sets that use the violet pairs for other purposes, like the 2830 which uses them for lines 7-9.To support 9 lines over a 25 pair cable, it's wired to maximize all the conductors it can. Some other sets do this as well, like the ITT 2861. For these phones, you can't use an 82b block, and need a separate cable wired directly into the phone's innards.

Some sets don't use the violet pairs at all, and leave those pins vacant on the 50 pin connectors, to save on metal presumably. For those, the station cable (wire that runs from the phone to the amphenol) can also be slightly thinner because it doesn't need to transport those unused conductors. Looks nicer, and easier to move the phone around on a desk with a thinner, more flexible cable.

Sometimes the unused pairs are used for special purposes by the phone installer; fun things like magnetic lock switches that open entry gates, patches into PA systems, alarms, bells, all kinds of stuff. Some executive type even talked a phone installer into wiring his desk phone to flush the toilet in his office's private bathroom using an unused pair to trigger an electric valve installed in the toilet. Installers would sometimes do all kinds of weird stuff with unused conductors in phones; it just means the 66 blocks have to be wired correctly to move those signals from the phone, and out to where they need to go.

[Greg Ercolano]

On 3/13/24 00:40, erco wrote:

On Wednesday, March 13, 2024 at 12:02:03 AM UTC-7 frot...@gmail.com wrote:

Looking at your copy of the 2565 manual, I see there are several signals in the purple group of lines that seem to be for indicators and signalling regarding speakerphone functionality.  Please tell me if I have this right: it's through that group that the phone interfaces with the speakerphone stuff by way of an 82B, and that a KSU from back-in-the-day would never actually touch those lines.

Yep, that's all correct!

Well, for 2565 sets anyways.. and any other sets that specifically support speakerphone features over the violet pairs.

Just to be clear, there are other phone sets that use the violet pairs for other purposes, like the 2830 which uses them for lines 7-9.To support 9 lines over a 25 pair cable, it's wired to maximize all the conductors it can. Some other sets do this as well, like the ITT 2861.

    I mention all that, not to be pendantic, but to indicate that the KSU might be wired to use the violet pairs for situations like the 2830, where the KSU might be providing all 9 lines to a 2830, or even 29 lines to a 2861.

    But for KSUs like the WECO 551 or Seriss KSUs, which really aren't meant for more than 4 CO lines, the violet pairs would definitely go unused by the KSU itself, unless there was some nutty special purpose wiring going on, which likely isn't provided by the KSU, but likely other external add on equipment that could be merged into the violet pairs at a 66 block.

[Greg Ercolano]

On 3/13/24 00:02, David Griffith wrote:

Looking at your copy of the 2565 manual, I see there are several signals in the purple group of lines that seem to be for indicators and signalling regarding speakerphone functionality.  Please tell me if I have this right: it's through that group that the phone interfaces with the speakerphone stuff by way of an 82B, and that a KSU from back-in-the-day would never actually touch those lines.

    Not sure how far down the 4A speakerphone rabbit hole you wanna go when looking into the signal paths, but here's a couple of interesting documents:

1. This is a pleasant, easy to read overview of the 4A speakerphone system, including a functional schematic, a nice technical description of how the circuit works, and a pic of the guys who built this system. The 82 block is also covered, which they describe as making a 4A speakerphone installation "almost as easy to install as plugging in an electric toaster":
   
   https://www.telephonecollectors.info/index.php/browse/catalogs-manuals-educational-docs-by-company/western-electric-bell-system/publications-and-educational-documents-by-date/blr/11684-73sep-blr-p233-4a-speakerphone/file
   
   
2. A full on schematic of the 4A speakerphone system. I have yet to find a description of all the signal names (e.g. "IT-P3", "IR-P4"), but I'm going to guess in this context where "T" and "R" show up a lot, it's not so much Tip and Ring, but Transmit and Receive. And indeed if one looks at the schematic to trace where those signal names go, it's sometimes obvious (e.g. "TVL" almost surely means "Transmitter VoLume"). There's also a different version of the 82 block wiring diagram on page 19:
   
   http://bellsystempractices.org/Miscellaneous/4A%20speakerphone%20scmatics%20SD_69909_01_I8D1_4ASpkr.pdf