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Bell 1A2 KTUs


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#1 systems_glitch

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Posted 24 August 2012 - 10:58 AM

I seem to have found the type of phone I'd like to use with my two lines at work: the Bell 1A2 multiline KTU. Problem is, these phones require an external KSU to provide voltage and signalling to the lamps and ringer/buzzer in the KTU. I've found the Bell documentation for various KSUs, and it doesn't look like there's a whole lot going on in there. Anyone have experience with KSUs, especially building your own?

#2 ThoughtPhreaker

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Posted 24 August 2012 - 05:54 PM

For what it's worth, it looks like the lamps within a key set are 10 volts.

http://www.lighting-...pos=8&pid=52935

I've played around with a few key systems from the mid 80's. I think the design had been pretty much changed by then - everything was microprocessor based.

#3 systems_glitch

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Posted 24 August 2012 - 07:09 PM

I had some time to look over the Bell manual at work...looks like it'll be pretty simple even if I have to wire up my own interface. Basically, you have:

  • Ring/Tip -- from the CO/FXS/ATA
  • A/A1 -- Closed when a line key is closed
  • L/LG -- Illuminates the lamp for a key

That repeats for as many lines as the phone will handle. Just driving the lamps would be pretty simple, but I'll have to see if I can come up with something a little more involved.

#4 ThoughtPhreaker

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Posted 24 August 2012 - 07:41 PM

Are you hooking this up to something with MWI capability? I vaguely remember there's a couple different implementations, one of which has a pair completely separate from the one carrying voice. You might want to see if that'll work with a 1A2 lamp.

#5 systems_glitch

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Posted 24 August 2012 - 07:57 PM

Yeah, at least one of the devices does (Digium IAXy). Apparently the HOLD button lamp is almost never used to indicate anything, so it would likely make a good MWI indicator.

Incidentally, I think I've actually got a 400-series KSU card. I picked it up at the MIT Flea because it had a really unusual metal can LED on it (and it was $0.50), but it looks a /lot/ like a 1:1 clone of ITT's 400 series card. I'll have to see if I can trace the circuit out well enough to confirm that (or just power it up and see if it smokes...I do know it's out of an old PBX).

#6 ThoughtPhreaker

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Posted 24 August 2012 - 08:12 PM

I was thinking if you knew what triggered the MWI flash in software, you could have the indicator go off based on something else - like an incoming call. A quick Google search says MWI pulses are apparently 90 volts. I'm not all that familiar with electrical components, but if that's true, couldn't you put in a few resistors to drive the bulbs?

#7 JmanA9

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Posted 26 August 2012 - 09:31 AM

In case you haven't seen this site, do a CTRL+F for "key" and you'll find several documents that may be helpful:

http://thephonebooth.../bsp/index.html

#8 systems_glitch

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Posted 27 August 2012 - 02:17 PM

In case you haven't seen this site, do a CTRL+F for "key" and you'll find several documents that may be helpful:

http://thephonebooth.../bsp/index.html

Yup, I'd come across their resources in Googling around -- good stuff!

I picked up a Western Electric 1A2 5-line key phone today, so experimenting will commence once it arrives. I've also got two known-good K400D line modules on the way (apparently only $1 each on eBay) -- shouldn't be hard to provide a breakout and power supplies for the modules, and build a solid-state interruptor for flashing lamps. I'd like to find a real Bell System KSU at some point though.

#9 systems_glitch

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Posted 06 September 2012 - 08:23 AM

Phone arrived yesterday! It's a modified Western Electric 2500 series from 1976. In pretty good condition...all of the buttons work, and it appears to be wired correctly. I was able to light the key lamps using a 9 Volt battery, and connecting tip/ring pairs to my Asterisk box allowed me to receive and originate calls.

I've been reading over the BSP for the phone...very good stuff. In addition to switching multiple lines to a handset and providing visual indication, you can remove a screw on the PU buttons and use them as momentary push without affecting the selected line. Of course, you can control each lamp independently. Screw terminals and a socket are also provided for the usually-nonilluminated red HOLD button, which will most likely get used as a MWI.

#10 ticom

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Posted 06 September 2012 - 09:15 PM

I'd like to find a real Bell System KSU at some point though.


Ask around your local communications companies. When I did that sort of thing not too long ago, we had lots of customers who were pulling those things out and dumpstering them, especially when remodeling the building.




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