Hi, fascinating stuff about exchange operation, I used to stick my head into the local exchange back in the 1960's and was gob smacked by all the relay things banging in and out and marvelled at the motor generator sets doing mysterious things!

Back to the "line compensation unit" I just wonder if it is exactly what it says: a mains regulator, that is it tends to maintain a "constant" output when the input varys over a range. I never quite worked out how they worked as they are a static transformer device using magnetics to um do something! The core of the transformer is a complex stamping with multiple windings. I assumed they either had a bucking coil system and/or had a saturated core section that sort of defied Mr Lenz's Law.

I did do some work on Magnetic Amplifers back in the day ( wound the cores) and saw personally voltage regulators work giving about 10% regulation using toroidal cores and one of the cores was the reference core being a smaller saturated device that acted like a Zener. The assembly had a recognisable Reference, Amplifier and Control sections but all done with Magnetics folks! NO electronics in sight.

All that technology disappeared over night when transistors arrived.
Fred.

Fred,
You could be correct as there were some devices within PMG/Telecom era that were called Line Conditioning units and the ones that I had encountered were simply a motor driven variac in which a small DC motor drove a variac to increase output volts if the mains dropped and decrease output volts if the incoming mains rose.

The DC motor was driven by a wee bit of solid state circuitry that sent the motor either forward or in reverse depending upon which way the incoming 240V supply went.
They reacted quite quickly and the resulting output volts were reasonably steady depending upon just how wide a range of input volts occurred.
Frequently found in radio comms sites to stabilse the incoming mains to some of the very early solid state transmitters & receivers mainly used in country locations where mains variations were a problem.

Stabilac was the name of one version. AWA did make also made one & in later years Trimax/Ericsson produced another version.

A picture would greatly help in identifying the possible use of the device in question.

Thanks for the accolade GTC...the ringing machines were always a focal point of any telephone exchange tour by school or other interested groups. There was a certain mystique about them sitting in a corner somewhere whirring away.

Lindsay

Yes I remember starting my telecom career in the Tamworth exchange in 1980. When they pulled all the crossbar switches out and went to axe the floor bowed up because it was pre stressed to carry the weight. They sold all the old gear for 100 bucks a ton and we dropped it into the back of the scrap yard truck from the 2nd floor.

Somewhere here, possibly in the Vintage Telephones forum there is a link to a tone generator which I think is located in a private museum. The video is on YouTube.

there is a link to a tone generator which I think is located in a private museum

This one: https://www.youtube.com/watch?v=VzIXvO6RahQ&list=PLgNzI09bRXtlv9-M7mrABEALyhplLpd-G&index=39

She's huge!

GTC,

That YouTube clip is of the more or less the standard sized ringer in most exchanges up to around 20-40,000 line capacity.

The AC output of the biggest was around 150Watts 75V 17Hz.

One did not need much current to ring a phone bell which was usually a 1000 ohm bell winding in series with a 1.8μF capacitor 75V 17Hz.

Two people were needed to safely lift the bigger ones off the Ringer rack being not so much heavy as plain awkward to get a decent grip on. Plus they were often very slippery if over lubricated...which was often the case.

Many of the smaller units used in country exchanges & PABX units (Private Auto Branch Exchange) such as many big companies had were much smaller units often around 25Watts & came equipped with a carry handle which made it much easier to swap units over when servicing was needed.
I dropped one once when I tripped on a slight step in a floor in a building, was not very popular with the boss at the time as it landed on its cross shaft & bent it badly & cracked the plate that carried the contact assemblies. It was duly packed up in a box & sent off to the PMG Workshops & came back weeks later all repaired & fully operational.

The big tone drum on the end had DC excitation coils wound in with the output coils around the stator poles and the rotors had teeth like pole pieces with the number of teeth on both rotor & stator setup to generate the different frequencies needed.

Effectively in that tone drum unit there were 3 alternators just generating tones (Dial Tone, Ring Tone & Busy/Nu-Tone).

The machines were the very heart of the switching machine as once that pair failed even though the switching plant could still switch calls there were no tones to feed to subscribers so when they lifted the handset to make a call..NO Dial tone. However if they did dial the required number it would still switch through and IF it was call that was to terminate in that same exchange the subscriber would get no tone back to show that ringing should be happening but should the called number pick up the handset the connection could be made through to speak.

IF the call was to leave that local exchange the call would switch via junction circuits & because the other exchanges around were not having a ringing machine failure calls would proceed normally.
Many subscribers NEVER listened for Dial Tone prior to dialing out so some would never initially be aware that the ringer had carked it.

Lindsay

Ok here’s a learning curve for me. Attempting photobucket links...

http://i787.photobucket.com/albums/yy158/muzzery/Mobile%20Uploads/B1689140-7FC6-4C59-8C27-C11963778116.jpg
http://i787.photobucket.com/albums/yy158/muzzery/Mobile%20Uploads/EF83ABE8-B1E7-4308-A938-7590ABB82F76.jpg
http://i787.photobucket.com/albums/yy158/muzzery/Mobile%20Uploads/FB79B80B-B812-4A63-AC96-AA8830CC9A54.jpg

Don't use Photobucket. Use Imgur, or better still email the images to Brad and he'll host them on here.

https://petapixel.com/2017/07/01/photobucket-just-broke-billions-photos-embedded-web/

Brad has now uploaded photos at the beginning of this post,. If anyone knows if this has a use, or historical value, let me know, I don’t want it, it’s more like scrap copper to my mind. I’m eager to get it out of my shed.
Murray

Hi all, the nameplate clearly says it all, its a 240 to 115 stepdown transformer and I would suspect it has magnetic core voltage control to give a "constant" output voltage to input variation. The unit clearly has only the core and a Heinmann circuit breaker in the box. Lovely bit of gear and surely someone has an application for it? I used a 500 watt size unit when I did a lot of testing of devices in my "lab". May be a ebay candidate?
Fred.

Thanks Fred.
I might throw it on the buy / sell section first .Someone on this nifty forum may benefit.
Murray