Photos of Phones and Phonographs (occasionally)

PAX Mega-Update, and a video.

To celebrate that I’ve got enough tie lines working to phone from one side of the living room to the other, via the asterisk server at the Dean Forest Railway.  I made a video of me dialling 30-0-50-91-491.

The red phone (GPO 706) is on my AT&E 50/7A PAX.

Dialing 30 takes you out through an outgoing tie line and onto the junction selector, 0 takes you back into the 50/7A on an incoming tie line, 50 takes you out through another tieline and into my asterisk server. 91 are the access digits which take you in to the asterisk server at the Dean Forest Railway, 491 then takes you back into my asterisk server, which then dials “39″ on your behalf which takes you out *another* tie line into my 10/2A PAX and then it finally dials a 5 to ring the black phone (also a 706)

Two 1950s strowger PAXes, a home-brew junction selector, two asterisk servers and a load of internet later – and I’ve phoned from one side of my front room to the other.

This is what happens when you throw your TV out and find something else to do with your evenings.

PAX Mega-Update!!!
As promised, here’s a list of everything I’ve done to my phone exchanges since I last wrote anything about them about 8 months ago.

My asterisk server blew up its HD controller, so I’ve completely rebuilt it, this time using a Neoware CA10 thin client (my power consumption has dropped from 60W to about 14W – win!) and a cheap and cheerful Chinaroby TDM400P which unlike most TDM400 clones can power the FXS ports without an external molex connector – which is handy because the CA10 doesn’t have any molex connectors inside!


In the process of doing this, I updated my build notes for the easiest way to go from bare metal -> debian -> asterisk/dahdi installed and working from packages in the repos (so you automatically get security updates!), with some basic OS hardening in the mix as well.  It doesn’t take much doing, is so much easier than building from source, and is more secure in the long term.  At some point I’ll finish the rant I’ve got brewing about why doing it any other way is madness!

I’ve also done a lot of work on the dialplan, built a prototype of a “Dial-a-Disc” macro although I’m not happy with it as it’s only got the long form of the announcement.  I’m working on a better replica.

I’ve done loads on the big exchange!

  • Back in March I had problems with FS4 not clearing down properly so I busied it out.  Until I found that entry in the exchane diary I’d forgotten about that fault.  I must fix it!
  • I ripped out the screw terminal DP I had in the bottom of the pax, and replaced it with a krone box.  OK, I know it’s not “heritage” but it is much more practical.


  • Terminated all 50 line circuits on the krone strips
  • Fitted a small panel of 6xRJ45 sockets, these are also terminated on the krone blocks, and are jumpered so that each RJ45 carries 4 extensions. 21-24, 25-28, 41-44, 45-48, 61-64, 65-68.  This way I can run cat-5 around the house and use adaptors to break it out to phone sockets.  The whole PAX is then self contained and not wired into my house.  Which will make moving it easier in the future.
  • The Asterisk junctions also terminated on the krone block, and are jumpered in to 51 (from the asterisk FXS) and 50 (to the asterisk FXO)
  • I wired my homebrew junction selector back in.  Again this is terminated on the krone strips, and is jumpered to 30 (to the junction selector) with outlet 0 jumpered to 31.
  • Exchange phone is now jumpered to 68 rather than 35 as it used to be.  This is brought out on a BT socket in the bottom of the PAX.
  • I’ve been right through all the odd strapping arrangements I found on my PAX back in 2011, I’ve worked out what all of them do apart from two lines – and have reversed all the strapping back to stock.
  • The two lines which are strapped strangely seem to go off to the FA tags, which are associated with the external fire alarm equipment (which I don’t have) and the FA relays in the selectors (which I also don’t have) – I’ve sunk a lot of time into failing to work out what’s going on there.  I’ll sink a lot more time before I give up and revert the strapping!
  • Cleaned and adjusted the RV and BV contacts, so the tones are a bit nicer now.

I’ve also been giving the small exchange some TLC

  • Sorted out the earthing, so if the PSU goes faulty it’s not going to kill the cat.
  • Modified Extension 0 for tie line working.  This involved an awful lot of chatter on the THG mailing list about how I should go about it (all I wanted to know was the dimensions of the standoffs for mounting the rectifiers!)  For info, they’re 6BA threaded stud to 2BA tapped hole.  The standoff is about 1″ total length, and each threaded portion is 0.25″ long.  They look like this (bare standoffs on the left, the ones fitted to my 50/7A – including the rectifiers – on the right):


  • I’ve hooked extension 0 up to the 50/7A using the tie line on 39.
  • I wired out all the extensions down to a set of RJ45 sockets in a similar manner to the 50/7A
  • I’ve fitted the line relays for the extra position 11 on the LF mult, but haven’t wired them as it’s not a comfortable PAX to work on.  I need to see if I can get the side off it or something to give me space to see where I’m prodding a soldering iron.

My really dinky 5 extension electronic PABX.  I’ve had a good rummage in this and have determined that extension 5 is completely dead, 2,3,4 are OK. Extn 1 gets tones, can dial and will ring if dialled – but there is no speech path.  This is either a really easy fix, or a really hard fix.  It all depends which component has gone bang and if I can get a replacement.  Once my workbench is clear of projects I’ll look at it properly.

One Response to “PAX Mega-Update, and a video.”

  1. Charlie says:

    congrats for making the b3ta newsletter as well!

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