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27/10/2021

Restored GPO 300 Series Bakelite Telephones

Some time ago I had a small collection of 70s era GPO 740 series rotary dial telephones which I sold for a pittance when I moved house, something I since regret. I recently started playing with analogue telephony again, and my suppressed passion for old telephones returned.

I picked up a couple cheap of 746s from EBay and Facebook Marketplace but it didn't quite scratch the itch. I needed a "proper" bakelite phone, so I picked up a 312 from Facebook Marketplace for £30 which is relatively cheap, but it turned out to have some damage to the bakelite shell. I then found a 332 at a car boot with a sticky dial for £25 and quickly ended up with another 332 in very poor condition for £17. Finally I picked up another 312 with a damanged handset at RetroTechUK for £20. 

So that left me with 4 phones in varying states of disrepair for £92 - not too far off the price you'd pay for a fully restored 300 series phone. But now I had to restore them.

I won't fully document the process here, but with some part swapping and some spares aquired both online and at a Telecommunications Heritage Group "Swap Meet" I was able to restore 3 of the 4 phones to their former glory for less than £60 each, which includes the cost of purchasing all 4 phones and the required spares - not bad!

I intend on getting hold of another phone in poor condition to document the actual restoration process, which I'll post once finished. In the meantime, enjoy the photos:

GPO 332, GPO 312, and GPO 332 with a Dummy Dial  

23/10/2021

Assistance required - Building a Dial-up Network Access Server. Cisco NM-30DM?

Hello! I currently have a project bubbling along in the background to provide multiple (100+) of copper telephone lines to a bunch of people in a field, for "fun". For added "fun", I'd quite like to be able to provide dial up internet, even if it's just for a handful of active users.  But this is a little out of my comfort zone, so I could do with some help!


Cisco NM-30DM Module
Cisco NM-30DM

30/09/2021

Sous PIDe v0.1

I've wanted to build a PID temperature controller for a while. It's essentially an intelligent thermostat that carefully maintains the temperature, with a low hysteresis and minimal overshoot. They're used for all sorts of things, like sous vide cooking, brewing, reflow solder ovens, basically anything where accurate temperature control is required.

I've recently done some experiements with Retrobrighting (bleaching) old discoloured ABS telephones. The original method involved using a source of UV, such as the Sun, but more recently people have had good results using heat, which finally gives me an excuse to build a PID temperature controller.

This post isn't a detailed tutorial. Just some food for thought if you're constructing your own.

Sous PIDe - A PID based temperature controller
 

15/08/2021

Telkom Telos ATP-1

As you may have guessed from previous posts I have a thing for phones. Recently someone on IRC going by the name of gannymac

Telos ATP-1 Phone

 

06/08/2021

Fixing Gai-Tronics Commander Telephone Speed Dial Memories

Some people might say I own too many phones. Those people are wrong. I've got a small collection of  Gai-Tronics phones and recently got one of the speed dial memory ones for £20. It's missing the handset cradle, so it's not quite fully operational.

Before I got around to testing it I saw a post on a forum stating that the memory speed dial versions of these phones tend to die prematurely. Someone else suggested it might be due to a dead battery.

I hooked it up and whilst inbound calls worked fine, sure enough the speed dial button didn't work. Hmm. Time to take it apart.


30/07/2021

Connecting a Telephone handset to a USB Sound Card

I have a bit of a thing for ruggedised telephones like the ones you see on railways and industrial settings. In the UK the main manufacture is Hubbel, formerly Gai Tronics, formely DAC...

Their phones cost a fortune new but occasionally pop up on EBay for reasonable prices, however they're usually in some state of disrepair and spare parts cost a fortune. £200 for a replacement handset for a £600 phone. Yikes! (Incidentally I suspect this is why the end up on EBay, it makes more sense to buy a new one than try to get spares)

For a long time I've wanted to create my own custom internal controller to replace any that are broken, with the added bonus of converting them to SIP. I had some concerns about interfacing the handset / reciever with a soundcard as telephones generally operate at a different impedance to your average speaker and microphone, so I connected one up as a proof of concept. 

I chucked a photo up on Twitter and it was suprisingly popular so I thought I'd document the process

29/07/2021

BG7TBL 88-108MHz FM BPF Band Pass Filter

I've recently been listening to Pirate and "DX" FM Broadcast radio so I purchased a BG7TBL 88-108M FM BPF Band Pass Filter Ebay and stuck it on the NanoVNA to check it out.

It tested out well, with less than 2dB loss in the passband and 30dB rejection below 50MHz and above 145 MHz. Not much else to say about it, I'm just sharing here for posterity.