Re: GPO Modems
 

Ten out of ten.

I only noticed when I was looking at the image earlier today. The giveaway is the cutout on the right-hand side to allow the handset cord to exit with the lid closed.

Re: GPO Modems
 

Seeing post number 7 reminded me of a company I worked for many many moons ago now long since defunct (Transdata Ltd). They had bought in a couple to "have a look at" if you know what I mean! They (within about 3-4 months I believe) came up with their own version namely the 307 & 307A acoustic couplers. Both very good in their own right (up to 300bd), we sold thousands of the things, mainly to the GPO! I remember testing 30-50 a day & then on Fridays sitting down with the duff ones & fixing them. I always thought the GPO one was far better built, it just looked right.

Re: GPO Modems
 

I use to have a set of 2B modems, in a '62' type rack, I bought them for scrap and used them in answer mode for the original Telstar BBS back in 1981/2. I had all of the circuit diagrams at one point. I will have a look but I haven't seen them for years and years.

I still have a few of the DM424X type modems and a few others. I also have an auto answer board for the Nightingale series of devices.