I've been researching the Conduit Sub-Assembly trying to identify the various parts, locating photos or other details if available. Eventually after searching the internet unsuccessfully I managed to locate the parts in my own photographic archives. The photos were taken by me during trips to the UK between 2009 and 2012. Sadly most of the parts in the photos were not the subject, but maybe on the next trip.

Update 2016:
I'm following up on this and as it turns out I haven't listed the size of the conduit.

The GPO called this Conduit No.2 apparently, a search of britishtelephones.com has the following passage:
"Provision is made in both the top, and bottom, of the case for the entry of 0.75in conduit."
"This wiring (whether the bell is attached to the telephone case or not) and the external lead-in must be enclosed in Conduit No. 2."

Therefore it appears that Conduit N0.2 is 3/4" Diameter or 19-20mm in metric.



DRG 90770 - Conduit Sub-Assembly
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The conduit - Inspection Tee and Inspection Elbow
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The Button Box
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The Conduit - Inspections Tee & Plug
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The Plug and Socket
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The Suppressor
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The Mem Fuse Box
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New links for Police Box & Police Post plans : (operative 29 July 2013)

Police Box Plans A3 :  http://www.mediafire.com/download/8vv62amp5aexmqt/Police_Box_A3_Plans.jpg

Police Post Plans A3 : http://www.mediafire.com/download/r3x8yfr21pym69a/Police-Post-A3-plans.jpg

Police Post plans and photos of signage : http://www.mediafire.com/download/60fxrczmabl4a5m/Police_Post.rar

Hope these help people on their projects.

I thought I would Upload the contents of the Rar file, these days forum can handle having images loaded after all.
These are good references, and should be visible instead of just a link to a file that can disappear.

The other drawings have been uploaded here before, and been put in different threads.
Both are General Arrangements for the GPO equipment for the PA2 Police Post (DRG PA363) and Police box.

Quote from: theukarchivist on Jul 29, 2013, 03:07 pm
Police Post plans and photos of signage : http://www.mediafire.com/download/60fxrczmabl4a5m/Police_Post.rar

This is Drawing 90324 - Sheet 1 - Rev F From 1965 Showing PA No.2 Signalling Unit.



This is Drawing 90324 - Sheet 2 - Rev E From 1965 Showing PA No.2 Signalling Unit.



Following the design details shown on the drawing creates this object.
This is just the shell, I haven't taken the time to model the internal components, because I wouldn't know where to start. Nothing is dimensioned and I haven't got any photos.  



You can see in the original installation photo of this police Post, that they more or less look like this up until sometime in the later life cycle where they were changed out for White Cast Box version.



These units were plugged into the conduit receptacle in the lower compartment for power, and the rest of the internal components are wired to the telephone, lights, bell etc...