Railway Telephones (SPTs)

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Sam Mansfield

May 4, 2022, 10:56:31 AMMay 4
to London Hackspace
Hi folks,

I volunteer for a miniature railway, who are looking for some weatherproof phones for a new section of track. The ideal ones to use, both in terms of mechanical requirements and looking the part, would be Network Rail's Signal Post Telephones (also known as SPTs, lineside and trackside phones), such as the one currently being used as an intercom outside the cage.

I was wondering if anyone had any information on where this came from, and how to source more?


- Sam


May 4, 2022, 12:39:21 PMMay 4
to London Hackspace
Hi Sam,

They pop up from time to time on eBay - the magic words you're looking for are "Gai-Tronics" "DAC" and "Hubble" (all the same company but there's been various rebrands and aquisitions) or sometimes they're listed as railway phones, british rail phones etc. They can go as cheaply as £20, £40-50 is reasonable, anything over £80 is too much IMO but I guess it depends how desperate you are. That said, how reliable do they need to be? If the railway can't operate without them working, or theres some other safety requirement, you might need to buy them new and they're £500+

If buying second hand one thing to look out for is the plastic handset hooks, you'll often see listings on ebay where it's been smashed off and they cost £300 to replace - because they will only sell them complete with a new handset to ensure "compatibility". With this in mind sometimes its worth picking up a non-working, beaten up phone just to get hold of a spare hook.

Here's a few I've found that seem reasonable, although you might need to collect them. Some sellers will post items but there's no protection provided by Facebook.

Out of curiosity do you already have a phone system to connect them to?

If you need any help give me a shout - I've repaired various versions of these phones and have a few spares.



May 4, 2022, 12:41:45 PMMay 4
to London Hackspace
Your best bet would be to enquire on railway enthusiasts forums.
This chap might be able to point you in the right direction:- https://www.youtube.com/watch?v=kSno6hPapM4 
Which miniature railway do you volunteer at?

On Wednesday, May 4, 2022 at 3:56:31 PM UTC+1 cyber...@gmail.com wrote:

Sam Mansfield

May 6, 2022, 5:21:22 PMMay 6
to london-h...@googlegroups.com
Those are some great suggestions, thanks both! Interestingly, I've
worked with Gai-Tronics emergency intercoms before, never occurred to
see if they manufacture anything along those lines.

We'll probably need in the region of half a dozen, so I'll keep an eye
out on eBay and Facebook over the next few months. While the phones
will be useful for communicating quickly, a train whistle is still by
far the easiest way of attracting attention for anything safety
critical, given the effective range of a few miles.

We currently have what's probably best described as an antique PBX.
It's entirely mechanical, consisting of a number of relays and what I
believe to be four Strowger switches. The unit doesn't seem to have
any identifying markings, but does feature a rather nice diagram on
the inside. From what I can tell, it supports 16 lines (albit with
rather odd numbering), though only two simultaneous calls. Given the
lack of rotary dials on the SPTs, it's likely we'd need some separate
system to handle the automatic dialling, possibly with some
connectivity to the existing PBX. I have a feeling something like a
Grandstream HT818 would do the trick nicely.

The railway in question is the East Herts Miniature Railway -

Sam Mansfield
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May 6, 2022, 7:52:30 PMMay 6
to London Hackspace
DAC / Gai-Tronics / Hubble make most (or all?) of the help/info points on the Underground too, as well as the SOS phones on the side of the road, and have a range of intrinsically safe phones for mines and oil rigs etc. They appear to have become the manufacturer if you want a phone for some kind of industrial application.

I think most of the mentioned phones will do pulse dialling - there's usually a jumper somewhere. Finding manuals for them can be a pain because there's 3000 different hardware revisions and its usually only the manuals for the more recent versions floating around, but you can usually figure it out.

The Grandstream ATAs are decent (And support pulse dialling) but the feature code to call between ports is set to ***7XX and isn't natively adjustable which is annoying. You can change the numbers using some dial plan hackery but I'm not sure if it would scale up to 8 lines. Integrating it with the existing PBX might be difficult too, I can't think of a straightforward way to do it without additional hardware.

I'd love to see some pictures of the PBX if there's any online any where? Likewise if you need any help with phone things give me a shout, I'm in Watford so not too far although I've not got any practical experience with electromechanical PBXs - yet.


Sam Mansfield

May 8, 2022, 5:30:37 AMMay 8
to london-h...@googlegroups.com
I stand corrected, the outer case has a sticker for "Plessey Communication Systems". I've taken some photos of the unit and the circuit diagram, https://imgur.com/a/Oc1AHhk

Richard Painting

May 8, 2022, 12:48:11 PMMay 8
to london-h...@googlegroups.com
I have been told that TFL are re-signalling the District Line so that it will be radio equipped so it might be an idea to get in touch them.

From: london-h...@googlegroups.com <london-h...@googlegroups.com> on behalf of Sam Mansfield <cyber...@gmail.com>
Sent: 08 May 2022 09:30
To: london-h...@googlegroups.com <london-h...@googlegroups.com>
Subject: Re: [london-hack-space] Re: Railway Telephones (SPTs)
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