Old analog telephone system question. (Comkey 416) has a str

I have this old Western Electric Comkey 416 (circa 1976) analog key telephone system in my house. With two primary sets and the remainder being slaves the system can handle 4 lines and 16 extensions. The sets all connect onto 66 blocks with 25 pair cable. Yes it's antiquated but it does music on hold and intercom and serves our needs.

Lately I have noticed something peculiar. If I'm speaking with another party and I put them on hold the system will stay on hold indefinitely. However if I put them on hold and they eventually hang up my system will eventually go back on hook by itself. How can it do this? As far as I know this is just a "dumb system. How could it know that the other party hung up and then to release the line. I seriously doubt that they had the technology to do this in 1975. Maybe someone (like an Ex telephone guy) might know if Western Electric could have built anything that sophisticated into this system in 1975 to detect anything like a kiss off, (I'm guessing) from the CO. Thanks, Lenny

 

Technology was quite a bit more advanced in the 1970s than most people realize.

I'm guessing it detects the DC level on the line. Not much other way it could work eh ?

No matter what kind of phone it is, it works by modulating DC, so therefore it must present a constant load, kinda like a class A amplifier.

When I was playing around with phones I found like 45 volts DC when hung up and usually 6 or 7 when talking. Even if the phone co regulates that voltage it can't be a high current source. When the other party hangs up, even if the voltage settles to the same level there is going to be quite a positive going transient on the line. It probably detects that.

Honestly I am no expert, just fooled around with it a bit in younger days. But really I can see no other way it could do that than to detect that transient.

 

[Jon Elson]

captainvideo462009@gmail.com wrote:

I have this old Western Electric Comkey 416 (circa 1976) analog key
telephone system in my house. With two primary sets and the remainder
being slaves the system can handle 4 lines and 16 extensions. The sets all
connect onto 66 blocks with 25 pair cable. Yes it's antiquated but it does
music on hold and intercom and serves our needs.

Lately I have noticed something peculiar. If I'm speaking with another
party and I put them on hold the system will stay on hold indefinitely.
However if I put them on hold and they eventually hang up my system will
eventually go back on hook by itself. How can it do this? As far as I know
this is just a "dumb system. How could it know that the other party hung
up and then to release the line. I seriously doubt that they had the
technology to do this in 1975. Maybe someone (like an Ex telephone guy)
might know if Western Electric could have built anything that
sophisticated into this system in 1975 to detect anything like a kiss off,
(I'm guessing) from the CO. Thanks, Lenny

There is a disconnect signal that is (at least in the US) a 750 ms reversal
of the talk battery. If you've ever held on when the other party got
disconnected and there was a loud thump-thump and then you got dial tone
back, that was the disconnect signal. Apparently, your KSU detects that
signal.

Jon

 

In movies etc. I have seen where when the other party hangs up you automatically get a new dial tone. Not so here, it just sits there.

But if it does do that, then it is a simple matter to detect the dial tone.

 

Thats interesting Jon. I'm going to look for that. Wouldn't have thought that such an old system would have recognized anything like that. And Jurb I too have never seen where you get dial tone back when someone hangs up. I think its purely theatrical. Lenny

 

[Jon Elson]

captainvideo462009@gmail.com wrote:

Thats interesting Jon. I'm going to look for that. Wouldn't have thought
that such an old system would have recognized anything like that. And Jurb
I too have never seen where you get dial tone back when someone hangs up.
I think its purely theatrical. Lenny

I think #5 ESS goes back to dial tone when the line is disconnected from the
calling party. Sometimes I hang on for a while to see if a disconnected
call call from a family member can reestablish the connection.

(And, I THINK we are still on #5 ESS, but the phone co. could have very well
swapped out the switch at some time.)


I know that my old answering machine will drop the line when it detects this
signal. I think my NEC PBX will drop hold on the line, too.

Jon

 

[junebug1701]

On Monday, March 21, 2016 at 4:59:55 PM UTC-5, captainvi...@gmail.com wrote:

I have this old Western Electric Comkey 416 (circa 1976) analog key telephone system in my house. With two primary sets and the remainder being slaves the system can handle 4 lines and 16 extensions. The sets all connect onto 66 blocks with 25 pair cable. Yes it's antiquated but it does music on hold and intercom and serves our needs.

Lately I have noticed something peculiar. If I'm speaking with another party and I put them on hold the system will stay on hold indefinitely. However if I put them on hold and they eventually hang up my system will eventually go back on hook by itself. How can it do this? As far as I know this is just a "dumb system. How could it know that the other party hung up and then to release the line. I seriously doubt that they had the technology to do this in 1975. Maybe someone (like an Ex telephone guy) might know if Western Electric could have built anything that sophisticated into this system in 1975 to detect anything like a kiss off, (I'm guessing) from the CO. Thanks, Lenny

I worked for a Bell System company in the '70's and '80's. There was (and still is) a signal called "answer supervision" that is pretty much a battery reversal as Jon Elson described earlier. All but the cheapest PBX and key systems of the time would recognize that signal when a party answered and hung up their phone.

 

[David Lesher]

captainvideo462009@gmail.com writes:

I have this old Western Electric Comkey 416 (circa 1976) analog key telepho=
ne system in my house. With two primary sets and the remainder being slaves=
the system can handle 4 lines and 16 extensions. The sets all connect onto=
66 blocks with 25 pair cable. Yes it's antiquated but it does music on hol=
d and intercom and serves our needs.= 20

Lately I have noticed something peculiar. If I'm speaking with another part=
y and I put them on hold the system will stay on hold indefinitely. However=
if I put them on hold and they eventually hang up my system will eventuall=
y go back on hook by itself. How can it do this? As far as I know this is j=
ust a "dumb system. How could it know that the other party hung up and then=
to release the line. I seriously doubt that they had the technology to do =
this in 1975. Maybe someone (like an Ex telephone guy) might know if Wester=
n Electric could have built anything that sophisticated into this system in=
1975 to detect anything like a kiss off, (I'm guessing) from the CO. Thank=
s, Lenny

An abandoned call...

When the far end abandons the call, that CO tells your local CO.
It in turns drops [not reverses] the DC loop current for [ISTM]
450 ms. That was sufficient to drop the HOLD relay on a 1A2 KSU
with 400D cards.

This caused grief later when Caller-ID arrived. On a 1AESS,
it would announce such with a short DC glitch as it disabled
incoming audio, poked in a BEEEEEP, and reconnected the
audio. While the drop was far shorter, some cards would
drop off hold. Newer 400G & 400H cards would not.


--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close..........................
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

 

On Monday, March 21, 2016 at 5:59:55 PM UTC-4, captainvi...@gmail.com wrote:

As far as I know this is just a "dumb system. How could it know that
the other party hung up and then to release the line. I seriously
doubt that they had the technology to do this in 1975.

I remember I was watching an old "Columbo" detective movie called "Death Lends A Hand" (1971) where the guest star "Robert Culp" kept bragging about how much better private investigative organizations were at (what was I guess) highest-end listening device technology than the police dept was.