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GPO No. 1

Started by wds, December 08, 2011, 02:00:56 PM

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Stephen Furley

Quote from: Wallphone on December 08, 2011, 08:11:42 PM
Like Larry said get a small screwdriver but what might work better is two small screwdrivers. Once you get the first one inserted right where the the split in the ring is, get the second one in next to it and start working it around. When you get far enough away from the first screw driver you should be able to flip the ring out of the recess with the first screw driver. Do you know what dial it is yet? The link you posted was for a Type 12. The Type 10 should have a patent number stamped on the finger wheel.
Doug Pav

Most No. 10 dials do not have the patent number; I've never seen one which does, but I have seen pictures of some early ones which did.  The very early No. 10 dials also had a smaller centre ring, which this one does not seem to have.  However, the back is black, which probably indicates a 'middle aged' No. 10, rather than a late one.

To tell a No. 10 dial from the front can be tricky.  The usual indication is the finger stop, on the 10 it is wider, and positioned so that there is a small gap between the back edge of it and the '0' hole when in normal position.  On the 12 it is narrower, and positioned so that the back edge just covers a very small part of the '0' hole.

The shape and position of the finger stop on this dial look like those of a No. 12, but it definitely not a No' 12 dial.  I'm not sure if a No. 12 finger stop can be mounted on a No. 10 dial, and if so what position it would be in, or if some versions of the No. 10 dial had a different finger stop from new to the ones which I've seen.  The British Telephones site does have a picture of what is claimed to be a No. 10 dial with this style of finger stop.

Another way to tell the dials apart would be to look at the dial plate under the finger wheel at about the 4 o'clock position.  On the No. 10 there is a pair of small holes which are an alternative mounting position for the finger stop, in roughly the same position as it would be on a WE dial.  It seems that this was used for just a couple of exchanges which had equipment which did not require such a long delay.  Modern digital exchanges will also work with it in this position.  This provision was removed on the No. 12, and later, dials.

If you can see the back of the dial then there's no doubt.  The copper 'star' washer marks this as being a 'slipping cam' type dial; none of the later 'trigger' type dials had this.  The No. 10 was the last 'normal' slipping cam dial.  There were one or two special purpose ones, but these were not fitted to 'normal' telephones.

Scrolling down this page:

shows some very early dials, and then front and back views of the four most common GPO dials, the 10, 12, 21 and 54a.  The difference between the slipping cam No. 10, and the trigger of the later dials is obvious from the back.

The No. 10 and 12 dials are compatible with each other.  My 150 candlestick came with a No. 12, but I later replaced it with a No. 10.  Other than the finger wheels, most parts of these dials are however not compatible with each other.  These dials mount via three lugs on the back; two of these have a 'dimple' which locates in a hole, and the third has a tapped hole for a retaining screw.

The No. 21 dial was introduced for the 706 set, in which it was mounted via a metal ring which clamped around it.  However, it still retained provision for the older mounting method, and so a new No. 21 dial could also be used in an older candlestick or Bakelite telephones.  The 21 was normally fitted with a plastic finger wheel, early ones were coloured and later ones clear, but they could also be fitted with the earlier metal type if a thicker spacer was used underneath it than the type used with older models.  This was done on payphones, and where a new dial was fitted to an old telephone.  Plastic finger wheels cannot be mounted on earlier dials, they are too thick.

The easiest way to recognise the No. 21 dial is by the very narrow finger stop with a straight back edge; it will have this even if a metal finger wheel is fitted.  Looking at the back, the dial has a black moulded plastic body, to which is attached a thick metal plate on which the components are mounted.  The No. 21 dial was in production for many years, and during that time changes were made; the design of the main plastic moulding was changed, and more parts were made of plastic.  There were at least two of these later versions, and the easiest way to recognise them is that the central 'hub' to which the finger wheel attaches was changed from brass to plastic.  I have versions where this is white and orange; the white one has a threaded brass insert to take a machine screw and the orange one is solid plastic and takes a self-tapping screw.  The 'orange' version also contains more plastic components.  While the original No. 21 dial was probably the best one made, my experience with these later ones has not been good.

The 54a was the final standard dial, and is made almost entirely of plastic.  It is very light, far lighter than the 21, which in turn was far lighter than the 10 and 12.  This dial has a white moulded plastic body, quite unlike the black one with a metal plate used on the 21.  Finger wheels and dial plates, and their retaining clip are compatible with the 12; the finger wheel mounts with a self-tapping screw as on the later 21 types.  The central hub is usually blue, and it is easy to strip the thread in it if the screw is over-tightened.  These dials seem to be more reliable than the later 'increased plastic' 21 types.  The 45a removed the original mounting method, and so cannot be used in pre-706 models.

As a general guide, the 10 was used in candlesticks, 162 and early 232 and 300 series models.  The 12 was used in later 232 and 300 series models and in a few very early 706s.  Most 706s had 21 dials, a few with coloured metal finger wheels, though I've only seen a handful of these.  Most had coloured plastic ones, though these were sometimes replaced by the clear plastic type.   746s always had clear plastic finger wheels, on 21, or later on 45a dials.  These would have been the original dial types, but of course later types could be fitted during refurbishment; 10 by 12 or 21, 12 by 21, 21 by 45a.  A later dial could also have been fitted if a CB (dial-less) model was converted for auto use at some time in its life.

Another page with much information on GPO dials:

There were many other dial types, though most were not used in standard telephones.


I finally got around to having the brass parts nickel plated.  The parts had already been nickeled before, but for some reason it was removed from the outside of the parts, but not the inside - that's how you could tell it was all nickel at one time.  Dennis Hallworth did the plating, and I think he out did himself this time.  The brass receiver was/is pretty dinged up, but it's so shiny now you don't even notice.  I doubt if Western Electrics nickel plating looked any better than this when it was new.