THE “ MECHANICS”  OF OUR HERITAGE

 (something I knocked up in 2003 )  whilst still a "field" CSE  (engineer)

When I started  my career with the GPO in the late 70’s ,as a young lad of 16  I only knew that I wanted to be a “telephone” engineer ,to be truthful I had absolutely no idea of what went on behind the  huge secretive doors of a Telephone Exchange and at that time had little interest in such matters , I wanted to get “ out there”  in my yellow van, into the big wide world and repair subscribers telephones in their houses .

So some 3 years later having completed my apprenticeship and become a newly (fully ?) qualified  “Electro- Mechanical” switch engineer (I did not have much say in the matter I seem to recall !)  I was packed off to my first Strowger exchange in South London (Sydenham SE26 , a short  spell in the MAC centre at Croydon then followed by Balham SW17) to spend the next 3 years in the Test Room running jumpers, all my earlier thoughts of yellow vans and subscribers were no more.

Electro Mechanical – what’s that ?  my family would ask ,in the blossoming days of the microchip the “quaint” old ways of the GPO ‘s Post Office Telephones department with their relays, armatures ,pawls and ratchets seemed a mile away from the modern ,go getting technological world of the 70’s and  80’s .

  Having passed through the “probation” period of the Test Room  and all its ancient ways (booking advice notes into ledgers by hand, phoning up accounts and hand writing out a list of “non payments” so I could go to the IDF and physically move a “link” between two tags to cut off and “TOS” the miscreants ,answering calls on “178” from the very external engineers that I once desired to become –in order to give them a “clip” on the MDF (a tone sent to line) in order that they could locate the “E” side in the street cabinet and many other such duties) I was finally granted a “section” of my own  -10 racks of group selectors – where I had to suddenly recall all the training I had done  3 years earlier  ! memories of “ Electro Mechanical what’s that “ ? rung in my ears  once more –(it was now nearly 1985 !)

  Fast Forward ……..(2003)

  Just before Christmas I had occasion (quite officially !) to empty a locker unopened since the engineer who held the keys left for pastures new (and unknown) many years ago .One of the items I came across was an unassuming grey metal box about  6 by 3 inches ,very heavy and solid with a standard telephone cord and a large black plastic button – A Sender No 1 .

  The Chronically Sick and Disabled persons Act 1970- empowered Local Authorities to provide and/or assist in providing special  telephone apparatus for use by the handicapped .

  The Sender No 1 was designed back in the early 70’s as an aid for disabled persons ( its sole function was to dial the operator on “100” ).

Upon taking a screwdriver to the box I was fascinated by the so simple but so complicated Electro Mechanical construction of this device all this to dial “100” - all this ? , when you look deeper it is so simple a design ,one relay ,one motor ,a set of gears and some dial springs ,no semi-conductors –to break down, no programming -to lose ,no “electronics” at all ,just a solid reliable mechanical device that “ did what it said on the tin “

  The device was really no more than a motor driven dial ,a metal frame held a small 9 volt motor which via a 3 cog gearbox drove the “dialling wheel” the strategically placed cut outs on which allowed the dialling.   The device could be used with any number of different telephones including loudspeaking ones so giving the widest chance of helping out anyone with restricted mobility preventing normal use of a dial .A fiendishly simple arrangement of  two cam driven  contacts and a relay allowed the motor to be started execute its purpose and then stop at the correct place (home) ready for the next “call” .

  Referring to figure 1

The negative  connection of the  motor and relay were  permanently connected to “9v”( usually a 10v power unit 53B) via a rectifier

 

 

 

Pressing the button on the top of the unit operated  contact  S (start) , this allowed the relay “R” to operate to +ve 9v . Contact R1 operated ,holding the relay  in its operated state via contact  MS  2  (allowing the button to be released)  and driving the motor by applying +9v to the motor via MS1 . Both MS1 and MS2 remain unoperated  until operated by a cam (see below).

Having successfully driven the “ dialling wheel” enough to pulse out the required “100” (more later)  a cam attached to the bottom of the wheel operated the motor stop switch MS . MS2 operating removed the self hold path for the relay ,therefore releasing R1 and the motor supply ,however the recently released R1 allowed the motor to continue to be driven via the now operated MS1 just enough for the cam to release its operationof MS and stop the motor in its normal home position –ready for the next “call”  A very basic but very clever use of relay/switch /motor . The “D”  dial and  “DON” dial off normal, contact springs were simply parallel connected across their relevant connections within the telephone used ,providing the same function as the contact springs within the telephone’s dial itself. A connection ST was provided for remote operation of other devices in tandem (+ve 9v out) once the main “button” S had been pushed . 

  No attempt was made in the design with regard to the application of a calling loop to line (ie picking up a handset) as depending upon the users level of mobility and the telephone in use ,this was controlled externally.

Fast Rewind……..(1970,s)

Back then ,there were no phones with “memories” no last number redial, all automated callmakers were mechanical – be it  punched card ,tape or relay driven .There were no wireless operated pendant alarms or the like ,pre programmed to dial emergency services ,nurses ,or carers ,The GPO in its infinite wisdom decided (rightly or wrongly ) that disabled persons should ONLY be able to dial “100” and then seek the assistance of the operator to make their calls ! (I wonder if they had to pay the full operator rate ?) ! They could of course invest in their own callmaker (card for instance) and then pre program (the cards) with numbers of importance (once again an Electro -Mechanical  device !) but this certainly was not GPO policy .

  What other Industry used or relied on Electro -mechanical techniques and devices (whatever the reason) for so long ? The Post Office designers of the day kept these processes going far longer than anyone else .The amusement machine –in particular Pinball Machines is a nice comparison ,originally very similar techniques were used including the same 3000 type relays and uniselectors as used by the GPO ,however by the late 70’s the machines were (apart from the flippers) 99% electronic – even “ jukeboxes” could not find a better or more efficient method of working until Phillips invented the CD !  The last Strowger exchange was still in use some  15-20 years later ! .

  Teleprinter technology did not move on until the end of its days ,yes we had the likes of the “Puma” and the “Cheetah” both more computer than Teleprinter , but even the British Government used in its military and defence networks mechanical Teleprinters right into the 90’s !

Therefore as I see it ,it is only “us”  the preservationists and the collectors of the telecommunications heritage movement that are keeping this ancient mechanical technology to the fore – (and so may it reign !)

  Fast forward again …….(back to 1985)

  I was fortunate to have charge of my group selectors for only 12 months as come 1986 I was informed that my entire exchange was to -quote “close” and become a “Concentrator” off of the “Processor” sited in the nearest adjacent exchange building –yes - System X  had arrived in South London !

Being only a lowly “T2A”  (it took at least 3 years to become a “TO” and only Technical Officers were to be trained in the new digital techniques !  ) I was offered the choice of going back into the Test Room to run jumpers for the rest of my days or transfer out of the exchange and go “external “ and yes I became the “Subs Apps” repair engineer I had always wanted to be at 16 !    I got my yellow van  ( HA Viva at first –soon replaced by a Morris Marina /Ital  ) and it stayed yellow right up until I was issued a Grey Transit ( one of those with the box on the back - yuck) , (Always wanted a Maestro but never got the chance ( .

  At that time a transformation between  the 700 telephone with all its variants and plans and the new modern pushbutton equipment, was ongoing. Also although trained on the 700 and all the corded PABX/PMBX systems ,key and lamps and other “business” equipment it was not long before Business and Residential lines were separated off  into different departments ,the day of the 700 was numbered and as a Residential Subscriber (by now Customer) Engineer I was introduced to the delights of the Plug in telephone and the “Special range” Did anyone actually want a Slimtel  (yuck again ) or an Astrophon  back then ?

  Maybe it’s because I spent so little time actually working with both Strowger switches  and  the 700 phone, that I want to keep both going ? after all what can beat the mechanics of a dial stepping the Electro-mechanics of  a selector ?

  Those were the days …..sigh

  Notes:

MAC- centre - Measurement and Analysis Centre- "super" engineers ! mobile team targeting problem exchanges - would have been great if it had lasted ! but alas no -sent back to the test room at  Balham !.

MDF- main distribution frame ( connected the exchange equipment to the street cables)

IDF  - intermediate distribution frame (in Strowger days controlled the supervisory/auxiliary functions of a line- by jumpering )

TOS – temporarily out of service (as in has not paid their bill !)

T2A – Technician 2 A – one up from the basic GPO staff grade of the day the T2B !  (apprentices entered as T2A upon successfully passing their apprenticeship) now B2 grade

TO -   Technical officer –the normal grade of fully qualified and experienced exchange engineers  -(only one away from management) not available to the “external” branch who had to make do with T1 –(technician 1st class , alas  –no longer exists) ST - (senior Technician -again no longer exists)  both replaced with the "coach" CSC grade .

 TO- the grade by which we were all supposed to aspire to ! (now C3 grade) you had to do 2 years of  TOIT - (TO in training) back then to get made up to the full grade .

PABX/PMBX – Private Automatic/Manual Branch Exchange –Switchboards to you and me !

178  -the no’ dialled by external engineers connecting them direct to the nearest Test Desk for coop with faults  and new lines (external engineers could ring the exchange direct)

Kevin Sanderson

Dedicated to all ex T1’s  who never did get their TO   ☺ bitter ? me never !  (2003)

 

PS - I ended up finally as a "C3" the new version of "TO" in 2005 after 20 years as an external

field engineer - (a mixture of my choice and circumstance ) see "about me" for details .