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Author Topic: Why a UAX was Better than a Non-Director Exchange.  (Read 704 times)

burakkucat

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Why a UAX was Better than a Non-Director Exchange.
« on: November 01, 2016, 06:23:16 PM »

Well over a year ago, when browsing through various categories on eBay, I came across a DVD entitled Telephone Service at Farway. It was the history of the Farway, Devon, telephone exchange between the years 1935 to 1995. I am an owner of a copy and it is interesting to watch.

Earlier this year I noticed that another DVD had been created, once again, by members of the THG (Telecommunications Heritage Group) and also with all profits going to charity. This latter DVD is titled Goodbye Strowger and documents the switch-over to a System X exchange at Hornchurch, Essex, in 1992. Needless to say I ordered a copy and it is another interesting watch.

When the latter DVD was delivered there were also a number of A4 sheets of information enclosed. Here follows my re-typing of just one of those documents (without any editorial corrections) . . .

Why was a UAX better than a Non-Director (ND) ?

This is not mentioned in the DVD, but it is worth noting.

The UAXs gave less trouble than their Strowger counterparts, the Non-Director exchanges. In some cases pre-war UAX equipment was still in service right up to their closure in the digital age, and still happily working.

Partly in the UAX's favour, traffic was less intense than the larger ND exchanges. But even the smaller SAX design, (UAX size on ND principles) had the ND weaknesses and did not match the UAX virtues.

The UAX scored because --

1. Cyclical use of switches evened the wear, cleaned the banks, and if a switch fault was present, a re-try call would succeed. First-choice, or early-choice, failure in a ND caused havoc.

2. The battery-testing principle in a UAX meant that a condition had to be PRESENT for a call to proceed. Whereas in a ND, the dis-testing principle meant that a dirty bank or a bad wiper would give a dual-connection. Crossed-lines were rarely reported in a UAX.

3. Nickel-silver was used for bank contacts in a UAX. A better choice than the brass contacts of a ND. Not only less corrosion and noise, but also less metal dust to enter the gaps in the bank, which could cause leakage and arcing.

4. The bank separators were originally paxolin in the UAX. Less likely to break down than the plastic separators of ND. When arcing occurred within the bank (metal dust), the plastic melted and compounded the problem. Turn out the lights, and sometimes the glow could be seen inside the bank.

5. Receiver-off lines were automatically "parked" in a UAX.

6. 4000-type switches (pah!) were never used in UAXs.

v.1.1 12/15
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licquorice

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Re: Why a UAX was Better than a Non-Director Exchange.
« Reply #1 on: November 01, 2016, 06:41:49 PM »

Interesting and valid summary of the advantages. Might have to treat myself to a dose of nostalgia. :)
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4candles

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Re: Why a UAX was Better than a Non-Director Exchange.
« Reply #2 on: November 02, 2016, 01:09:43 PM »

Sun shining, birds singing, door open, and the sweet aroma of molten solder - ah, halcyon days in the 70s.


It seemed the natural order of things at the time, but looking back I marvel at what Strowger designers achieved. But, I do agree with the comment above about 4000-type selectors. Pah indeed!
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sevenlayermuddle

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Re: Why a UAX was Better than a Non-Director Exchange.
« Reply #3 on: November 02, 2016, 04:31:14 PM »

We are approaching the time of year when I get invited to submit a letter to Santa, I may well include the ebay link in that letter.

Question would be, we'll probably have various in-laws and Aunts in attendance...  Should I invite the whole family to watch it with me, as alternative to the usual festive broadcasts?  :D

Hasten to add, I have had no career connection to that BT/GPO technology, other than hanging around outside the local exchange at tea time as a teenager, pleading with the returning engineers to give me any spare or broken bits of equipment they had accumulated that day. :blush:
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Pellseinydd

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Re: Why a UAX was Better than a Non-Director Exchange.
« Reply #4 on: February 01, 2017, 03:24:52 PM »

<Snip>
The UAXs gave less trouble than their Strowger counterparts, the Non-Director exchanges. In some cases pre-war UAX equipment was still in service right up to their closure in the digital age, and still happily working.

Partly in the UAX's favour, traffic was less intense than the larger ND exchanges. But even the smaller SAX design, (UAX size on ND principles) had the ND weaknesses and did not match the UAX virtues.

The UAX scored because --

1. Cyclical use of switches evened the wear, cleaned the banks, and if a switch fault was present, a re-try call would succeed. First-choice, or early-choice, failure in a ND caused havoc.

2. The battery-testing principle in a UAX meant that a condition had to be PRESENT for a call to proceed. Whereas in a ND, the dis-testing principle meant that a dirty bank or a bad wiper would give a dual-connection. Crossed-lines were rarely reported in a UAX.

3. Nickel-silver was used for bank contacts in a UAX. A better choice than the brass contacts of a ND. Not only less corrosion and noise, but also less metal dust to enter the gaps in the bank, which could cause leakage and arcing.

4. The bank separators were originally paxolin in the UAX. Less likely to break down than the plastic separators of ND. When arcing occurred within the bank (metal dust), the plastic melted and compounded the problem. Turn out the lights, and sometimes the glow could be seen inside the bank.

5. Receiver-off lines were automatically "parked" in a UAX.

6. 4000-type switches (pah!) were never used in UAXs.

v.1.1 12/15[/tt]

Interesting!   Re 3 & 4    I've own several former  ex-GPO UAXs including the oldest one still in use - A UAX5 that served a village in Northumberland from 1929 to 1950, a pre-STD UAX12, a couple of STD versions and a few UAX13 racks from the 1960/80's - twenty+ racks in all. But none have nickel silver bank contacts for the selectors and all do they have Paxolin insulation for the bank contacts - even the later racks. 

Might interest you to know that there are still quite a few UAXs still working. They have been preserved and are connected to our replica of the old GPO UK network as it was back in the early days of STD. London is still reached with 01-xxx xxxx and Leeds with 0532 or Sheffield 0742. International is still 010 plus country code and the country's old STD/Area code and numbering. The old GPO Speaking Clock with Pat Symmonds (the voice of the 1960/80's) is still on 846/TIM in Director areas (London, Birmingham etc) or 8081 in the rest of the country. The old Post Office 'Radiophone' codes in the 003X range are used for numbers on our 'smartphones' .
If I dial 010 61 3 1194  I reach the original Australian Speaking Clock now preserved and still running in the Telecoms Museum in Melbourne!  Network reaches into over twenty countries - all the calls are free and there is no line rental!!  I administer the network in the UK (and most of the rest of the World except North America) 

You can find the old Speaking Clock still working on 01352 83 8081 or a more interesting version still working on an exchange on the road from Aberdeen to Braemar that passes by Balmoral Castle, is on 01330 55 8081   ;)   Probably a 'free' call in most call packages as they are normal 'landline' numbers and just as accurate as BT's 50+p call to 'Timeline'.

 How the Internet has changed our World!

Ian
0352 2345 or 0037 2979
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