EVEN MORE Retrobright Experiements - Restoring an Ivory GPO 746 Telephone

I've been doing some experiments with Retrobright recently, a process which uses Hydrogen Peroxide to bleach plastic back to it's original colour. Firstly I experimented with how temperature and concentration affected the bleaching process (link), and once that was complete I experimented with how time affects the process (link). I didn't make any groundbreaking discoveries but I've settled on using 3% H2O2 at 40°C without any laundry oxidizer going forward.

As I still had the equipment out and surplus H2O2 I thought I'd bleach an entire phone. I've bleached phones before but I'm terrible at taking before / after photos but this time I remembered, just - you'll notice the before picture is missing the handset cord because I forgot to take a photo before starting to strip it. Doh!

I picked this phone up along with another for a grand total of £5. I intended to strip it for spares but as it turned out to be an "8746" (It already has the required mods to work on a modern line) I thought I'd keep it intact. Here it is pre-bleaching. It's very, very yellow.



More Retrobright experiments

I recently did some experiments with Retrobrighting plastics, using Hydrogen Peroxide to bleach them back to their original colour. I wanted to see how temperature and concentration affected the process. Once I'd gathered the results I wanted to run another experiment to see the affect of time.


Retrobright Experiments

Retrobright, also known as Retr0bright is a process of bleaching sun damaged ABS plastic back to the original colour using a solution of Hydrogen Peroxide and laundry oxidixer containing TAED. It was originally developed for restoring retro computers which left the factory an off-white / light beige colour and often went yellow or even brown with age.

As you may know I've started collecting / restoring old telephones and the ABS plastic the GPO used to make phones in the 60s onwards also suffered from the same yellowing issue. It's most obvious on the Ivory models (Frequently sold incorrectly as "Yellow") but also affects the appearance of the coloured models, most notably the green and grey versions.

I've retrobrighted a couple using UV light, but in the UK the sun is variable and almost non-existant in winter, so I thought I'd try using heat instead of UV, and do some testing with different concentrations, temperatures, and amounts of oxidizer.







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  


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

Update: I've managed to get a working setup with the help of some clever folks from ShadyTel. It's currently in the testing phase - I'll do a full blog post soon.


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


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