Author Topic: GPO 1/764 pushbutton - A surprising oops moment!!  (Read 843 times)

Offline twocvbloke

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GPO 1/764 pushbutton - A surprising oops moment!!
« on: May 22, 2019, 03:34:51 AM »
Ever place a non-serious bid on something fully expecting to be out-bid long before the end of the ebay auction? Yeah, I did that this morning, and won, with no competition it seems... :o

https://www.ebay.co.uk/itm/323809171531

Won for a whopping 1 (Plus 5.50 P&P). It has to be the cheapest phone I have ever won on ebay!!! :o

So what is the GPO 1/764, well, it's their early attempt at a push-button dial telephone, given that North America had established the likes of the WE 1500 & 2500 designs, the GPO thought they best have a go with a domestic button dial too basing it upon the already well-established 746, though compared to the WE phones, this was quite a kludge!! It is pulse-dial only as they hadn't discovered DTMF just yet, requires a "Battery, Secondary No.22" 4.8v battery pack* to power the dial, so no line-power ability like the later 756 (therefore, dead or no battery, no dialling ability!), and recharges said battery while the phone is on-hook...

https://britishtelephones.com/t764.htm
* https://britishtelephones.com/batsec22.htm

And it's the latter that caught my eye, given my Trimphone dial LED illumination ideas, I wanted to see how the line-chargers worked, so I saw that and thought I'd have a go at it, and, well, it's mine! ;D

Anyway, observations on the phone, the usual yellowing has occurred, for some reason the bracket on the rear that holds the shell, handset and line cables has been broken off, and of course missing the battery pack (a good thing really, leakage of old cells is bad). I can't tell if the shell is damaged as it looks like the rear bracket was snapped off with brute force, but for 1 I'm not going to complain... ;D

Anyway, obligatory auction pics time... :)
« Last Edit: May 22, 2019, 06:40:12 AM by twocvbloke »

Offline FABphones

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #1 on: May 22, 2019, 05:31:40 AM »
Yay, you got another phone to play with! Bargain.
A 1 fish phone!    ;D

I look forward to reading more when it arrives.

Mine (8756) was yellowed too, I chemically sanded it:
http://www.classicrotaryphones.com/forum/index.php?&topic=20579

Your battery comments got me looking at my 1983 version. At first glance, from the top view, it could be mistaken to be the same phone, so if I may, photos of the 8756 base and interior for comparison:
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I don't collect Red Phones  ...they are starting to collect me
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Vintage Phones - 10% man made, 90% Tribble

Offline twocvbloke

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #2 on: May 22, 2019, 06:56:34 AM »
I really wasn't expecting to have won that phone, so I'm rather pleased with the price, and it's got features I've not seen before so it's something new to play with... ;D

Also I just realised I called the 756 the 754 (no such model existed!), corrected that error now!!! ;D

It'll be interesting to see the differences between the 756 and 764, though one obvious thing, there's a lot less spaghetti in the 756, but as I said, the 764 was a kludge of a phone, given a battery really wasn't needed as the technology for line-powered button dials existed, though I am interested to see how they put together the electronic parts for storing the button presses, given the 70s was the start of the microcomputer boom era...

And as for whitening, I bought a bunch of 1 Watt Royal Blue LEDs (useable for UV exposure as they emit near-UV light) last year which can be used for indoor peroxide-whitening, so may assemble myself an exposure box with the LEDs inside, I have a number of yellowed plastics I would like to whiten, I just haven't gotten around to making a suitable setup yet... :)

Offline andy1702

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #3 on: May 25, 2019, 04:18:21 PM »
I just posted in the Trimphone thread about these phones with the battery inside. I didn't know they recharged. Am I remembering right that some phones had a blue battery and some had a red battery, which was different somehow?

Good luck with the experimentation. I'm looking forward to someone coming up with a way of powering a trimphone dial.

Incidentally, don't later model US Trimline phones have an illuminated dial powered by the line? I know early examples had a mains powered transformer and tungsten bulb, but from what I've read the later ones had a line powered LED of some kind. One of those might give some clues on how to light a trimphone?

Unfortunately US Trimlines are very few and far between over here.
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Offline twocvbloke

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #4 on: May 25, 2019, 04:49:55 PM »
The battery difference is Red (Battery, Secondary No. 22) = 4.8 Volts, Blue (Batt. etc. No.23) = 7.2 Volts, and denoted by the phone model, 1/764 being No.22 and 2/764 being No.23... :)

Plenty info on the phone in the usual place on the phone and its' charging arrangements (can be line, can be a local 50v supply):
https://britishtelephones.com/t764.htm
(I should have posted that initially but I forgot!)

I'm looking forward to seeing how it works though, I knew of them but never really looked into getting one of these phones for interest purposes, but with the thoughts on Trimphone dial lighting it just popped into my head when I saw this particular phone for sale, I guess it was just fate that my not-serious bid actually won it for me...  ;D

I was hoping the phone would have arrived today though, but unfortunately not, have to wait until Tues. with it being a bank holiday Monday...  :-\

As for the Trimlines with LED-lit keypads, I presume they only light when off-hook (as on-hook they're sat in their base cradle), so are presumably taking power from the line when in use, and when on-hook, they're cut off so they don't take a hit from the 48vDC line power, that's all I can deduce without knowing though... ???

Offline andy1702

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #5 on: May 26, 2019, 07:24:23 AM »

As for the Trimlines with LED-lit keypads, I presume they only light when off-hook (as on-hook they're sat in their base cradle), so are presumably taking power from the line when in use, and when on-hook, they're cut off so they don't take a hit from the 48vDC line power, that's all I can deduce without knowing though... ???

I think you're right. I gather a Trimline only lights up when off-hook. I don't actiually have one (yet) so can't tell you much about it.
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Offline twocvbloke

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #6 on: May 26, 2019, 10:09:11 AM »
Well, seems Hermes delivers on a Sunday, as the phone is here, haven't taken pictures as yet, but am presently fondling those buttons, ooh they have a nice feel to them, almost akin to an IBM model M keyboard, but without the clicky sound, really nice action on them...  ;D

Need to grab the N-diagram for it as there's a couple of loose wires which I've no idea where they go, and of course the rear bracket needs a replacement from somewhere, but overall it's in reasonable shape, which for 1 is an absolute steal!!  :D

Offline Jim Stettler

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #7 on: May 26, 2019, 11:19:31 AM »
You should nominate it for find of the month.
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Offline twocvbloke

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #8 on: May 26, 2019, 11:31:33 AM »
I hadn't thought of that, certainly been a find for me, just working out how to fix it at the moment... :)

Offline twocvbloke

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #9 on: May 26, 2019, 04:07:46 PM »
Just been taking pictures (not processed them as yet) and taking the phone apart, and I've noted a few things about it...

One is a Mercury Wetted Contact Relay, definitely something you wouldn't see being used today!!
There were no feet or a rubber plug in the auxiliary wiring hole, which leads me to believe this was actually used atop an N625 base...
The dial, I can't work that out, there's no IC on there (not surprising) so has to be entirely run through the various transistors, diodes, capacitors and resistors, very complex, and confusing, I don't dare even think of taking the dial apart!!!
The handset is outfitted with a blue Transmitter 21/A which I believe is Rathdown Industries...

I decided my chocolate brown 740 is to be parts, considering when I took its' case off, the cracks I'd glued up broke apart again, so, the shell's just spare plastic I guess, and I'd previously nabbed some innards already, so, parts phone...

Drilled out the remains of the bracket from the 764, and removed the 740's in the same manner, had to file down the smallest of my pop-rivets to fit through the holes in the base plate, and the bracket holes needed opening up somewhat to accept said rivets, but that attached nicely and looks pretty good if I do say so myself, haven't test-fitted the shell as yet as that and the other plastics are presently having a bath, as is the handset cable which is pretty stretched out...

About all there is to report so far, and now I'm quite hungry so I shall get myself some food, then work on processing the pictures... :)

Offline Babybearjs

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #10 on: May 26, 2019, 06:29:06 PM »
Thank you for posting the pictures. Big difference in design for the dial! I'm so used to WE equipment that seeing a GPO phone is really a treat! the keypad is soooo huge! wow!
John

Offline twocvbloke

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #11 on: May 26, 2019, 07:16:26 PM »
I just got the phone back together, and now I want to grab one of my 2500s to compare dial sizes now!!!! ;D

Still not done my pics yet though.......

Offline twocvbloke

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #12 on: May 26, 2019, 09:24:20 PM »
And at long last, pictures, taking it apart pre-washing and noting a few details of the phone:

Offline twocvbloke

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #13 on: May 26, 2019, 09:27:40 PM »
And 2nd lot of pics, replacement of the bracket, addition of feet & aux. wiring plug (and the addition of a scratch from some berk with a screwdriver!), a home-made screw retention nut made from a large, cut-down, filed and threaded rivet, and lastly the final thing, even though I haven't actually wired it up yet, and a chocolate brown handset sat atop it...  :)

(last two are just bigger versions of two in set H for clarity)

Offline Babybearjs

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Re: GPO 1/764 pushbutton - A surprising oops moment!!
« Reply #14 on: May 26, 2019, 09:40:15 PM »
Oh I hate that when that happens... a piece breaks off and its part of the housing... so frustrating fixing parts like that!
John