House Exchange System 2

[Dave Moll]

I have recently acquired an HES2 Telephone Intercom 1/2(A) (aka "Crocodile" telephone), and would be interested in any wiring information that is available concerning these systems - even though I currently have just a single 'phone and no switching unit. With access to wiring instructions, my hope is to determine whether it would be feasible for me to "home-brew" a rudimentary set-up to demonstrate the unit I have rather than for it to be a display-only item.

As always, any assistance would be appreciated.

[AndiiT]

Hi,
Might this be of any help?

I have successfully wired a HES4 and HES3 intercom phones to work on a single line, so can see no reason why you shouldn't be able to achieve this with a HES 2 terminal.

Regards

Andrew

[Herald1360]

That's one of those diagrams that's no doubt perfectly correct but looks about as helpful as a picture of a plate of spaghetti.

[Dave Moll]

Thanks, Andrew. I'll get out a fork and try to unravel the "spaghetti".

By the way, I may get back to you some time about my HES4 'phones, but that's a project for another day.

[AndiiT]

Hi,
Am I correct in thinking that the HES2 is a two line system the same as the HES4? If so the bell ringing on an incoming call might be an issue if you are planning to use two independent phone lines on the "beast"

With the HES4 there was a relay set that directed the ringing current to the bell depending on which line was being rung so I guess that the HES 2 intercom may be similar, or more likely seperate independant belss may have been used.

I haven't reall taken a proper look at the Spaghetti diagram yet to see if I can make any sense of it.

Regards

Andrew

[OscarFoxtrot]

The exchange line in are shown in this diagram

http://www.samhallas.co.uk/repositor...grams/Q216.pdf

The index to the HES diagrams is here
http://www.samhallas.co.uk/repositor...grams/Q100.pdf

[Dave Moll]

Andrew: the HES2 is indeed a two-line system, and ringing for an incoming call without the switching unit may be a case of using an external bell. The unit I have doesn't have an internal bell as far as I can see, just a DC buzzer which is presumably energised from the switching unit.

I have identified what appear to be the two exchange line inputs, but connecting either of them to a line doesn't seem to do anything - even if I try manually operating the internal relays at the same time as depressing the appropriate exchange button.

OscarFoxtrot: thanks for the additional information, which may help to identify further connections required to make this function.

[Dave Moll]

OK. Ignore my above comment about line connections not doing anything. I thought I had tried each line pair with each exchange button/relay, but I now find that depressing the appropriate exchange button and operating its associated relay gives me a dial tone. Applying 50V between pairs 13/14 and 15/16 holds the appropriate relay electrically if I operate it manually. The final step of this phase is to try to get the relay to operate without manual intervention - though it may be that the 50V output from my telephone tester is simply unable to deliver sufficient current. For information, pair 1/2 is the connection for line 2 and pair 5/6 for line 1. There is also provision for an extension bell on pair 11/12, though I haven't yet established under what conditions that would ring.

Phase two will be to hook further extensions to work on an intercom basis. I have established that extension 1 connects to pair 19/20, extn. 2 to 21/22 through to extn. 10 on 37/38.

... so I'm quite pleased with the progresss so far.

[Dave Moll]

Originally Posted by Dave Moll

it may be that the 50V output from my telephone tester is simply unable to deliver sufficient current.

I think I've eliminated that possibility - the voltage going into the 'phone remains rock steady at 50V with not the slightest quiver on pressing the line key or manually operating the relay. So, I'm a bit stumped.

edit: applying 50V direct to the relay operates it successfully, so a loss is occurring somewhere within the internals.

curiouser and curiouser: applying the 50V to the correct input, the relay is only energised once it has been operated! 0V is present across the relay coil until I depress the armature, whereupon 50V appears. My brain hurts!

[OscarFoxtrot]

Originally Posted by Dave Moll

curiouser and curiouser: applying the 50V to the correct input, the relay is only energised once it has been operated! 0V is present across the relay coil until I depress the armature, whereupon 50V appears. My brain hurts!

That's standard for a latching circuit. There must be another contact or button elsewhere (in parallel with the relay contact) which would apply temporary 50V to the relay, the relay will then latch on.

[OscarFoxtrot]

http://www.reuk.co.uk/OtherImages/ma...dpst-relay.jpg

push to make energises the relay coil, contact AB holds the relay operated, contact CD switches something else. push to break will relerase the relay

[Dave Moll]

Latching with a "push to make" button would make sense except that the exchange selection is by a latching button, but a further connection needs to be made before this is able to select a line.

I think, however, that I've worked out what is going on. Following on from the exchange A&B terminals, there are two more terminals, labelled C&D. If C is earthed, it operates the buzzer, and D needs to be earthed for the relay to operate. I assume that this is normally done in the switching unit, but that the earth connection to D is broken if the line is in use from another telephone on the system - thus preventing selection of an exchange line that is engaged. Because the relay remains energised if this earth connection is broken while it's energised, the line is only released once the telephone goes on-hook, preventing interruption of a call in progress. Presumably, when the switching unit detects that a loop has been made on an exchange line, it breaks all these earth connections on that line.

Does the above seem a reasonable conjecture? If I can find a wiring diagram for the switching unit I can presumably see how it's actually done.

I have also established that I can communicate with a telephone connected to one of the ten extension circuits.

[AndiiT]

Hi,
Here is the diagram to the switching unit (I think). Once again I'm afraid that it's "Spaghettified" but that's not my fault

I'm not certain if the Call transfer unit, to give it the correct title, was actually required unless a non - multiple (i.e. two-wire) telephone was used as one of the "stations".
I'm more clued up on the later HES3 and HES4 systems to be fair and that was only from having to work out the wiring for these to be able to use them in my own set up/display.

Dave, I think that you are quite correct in figuring our that the line(s) on the telephone stations are "daisy chained" in such a way that once an exchange button is pressed all other phones are prevented from seizing that line by accident, in the later HES3 and 4 designs their were supervisory lamps fitted to prevent this happening but it seems reasonable that the relays in each station could be responsible for preventing this in your HES2.

In the later systems the exchange lines were still daisy chained but there may have been a common relay set somewhere in the system to prioritise exchange line selection.

The HES2 must be a 2 line ten extension system as is/was the later HES4

Regards

Andrew

[Dave Moll]

Thanks for the pointer to the diagram for the transfer unit. I'll have a rummage through that and try to make sense of it.

Meanwhile, having tested the thing successfully with croc clips everywhere, I'm now in the process of wiring it up on a more permanent basis.

[AndiiT]

Hi again,
Having had a longer think about this, is it possible that the D wire to the relay(s) is earthed from a springset on what would normally be the "next" station(s) down the line ,as it were, thus allowing the exchange button on the desired station to select the appropriate line? (if you understand what I mean).

The buzzers in the stations would probably just quite simply be wired between the 50 volt line and the necessary calling keys on the other stations.

Regards

Andrew

[Dave Moll]

Thanks to those who have helped, I now have the speech circuits all working as they should - for the time being I just have both D wires strapped to earth on the basis that I currently have no other stations competing for the exchange lines.

I would now like to turn my attention to signalling. As far as detecting an incoming call from an exchange line is concerned, I'll just place a signalling device across the line - probably including a visual indicator using a neon so that I know which line is calling, and with a capacitor of course. Given that there is a single buzzer (plus optional extension bell) and no indicators specific to an exchange line or extension, I'm unclear how the station would have originally known from where it was being contacted.

For the purposes of my demonstration setup, I shall use standard 'phones for the extensions, which will really only be usable to receive incoming calls from the HES2 station. Given that line voltage is only be applied to them when they are selected, I could wire in a DC signalling device that is only in circuit when the extension is on-hook.

Finally, a couple of minor additional points: first, there are three connections on the cable whose purpose I've yet to identify; they are labelled respectively "R" "HL" and "COM". I assume that the last stands for "common", possibly as a return for the other two. Finally, I have been assuming that "battery" refers to a 50V supply. Is this a reasonable assumption, or could I be stressing components (such as relays) by running them at this voltage?

[OscarFoxtrot]

Originally Posted by Dave Moll

Given that there is a single buzzer (plus optional extension bell) and no indicators specific to an exchange line or extension, I'm unclear how the station would have originally known from where it was being contacted....Finally, I have been assuming that "battery" refers to a 50V
supply. Is this a reasonable assumption, or could I be stressing components (such as relays) by running them at this voltage?

It appears that incoming calls would usually be answered at the 'master' which has a Transfer Unit with (an) exchange line indicator(s).

Incoming call signalling to other stations is by extension of the exchange line or external extension alarm bells. "On installations having two exchange lines a common alarm bell serves both exchange indicators, so that when the alarm circuit is extended it becomes necessary to test both lines at the normal internal extension."
http://www.britishtelephones.com/eri...etin/11_15.htm

"Testing" appears to be pressing the exchange line button before lifting the handset, and the station buzzer would indicate an engaged condition.

The power is normally obtained over a power lead from the public exchange but where this is not available a battery of primary cells or a trickle-charged accumulator set may be employed. The system is designed to operate on 24 volts but the factor of safety is sufficient to permit its use on any voltage between 18 and 28 volts. The maximum current consumption is approximately 1.3 amps. for a fully equipped (10 + 2) installation. A 10 uF condenser should be connected across the power lead in order to reduce to a minimum any crosstalk due to battery feeder resistance.
(source as above)

NB House Exchange Systems 3 and 4 operate on 50v power.

[Dave Moll]

Thanks for that information. The linked page seems, from a cursory skim of it, to answer a lot of my questions. I shall go away and have a careful read of it.

[OscarFoxtrot]

I'm just adding to this thread as a convenient place.

I didn't know HES1 and HES2 were ever made in colours other than black, but there's an ivory one for sale.

Also notable is this one was apparently used in a house, with an associated flat and where a secretary was employed.

https://www.vintage-radio.net/forum/...pictureid=3168

https://www.vintage-radio.net/forum/...pictureid=3169

[Aaamusements]

Someone on one of the ubiquitous antiques programmes bought and sold one of the phones on the link in post 17. I can't remember what was paid and what they achieved at auction now.