The Test Mule


The Test Mule

I’m not sure exactly where the idea came from. I suppose it is like most others, a tiny little grain of a thought gets stuck in your head and layers of ideas form around it. There were quite a few things along the way that needed to be solved.

Years ago I reverse-engineered the strange auxiliary inputs of the Datsun/Clarion radios. They have 5-pin DIN connectors on the back of certain radios. I blew up a few of them trying to feed a signal into them. After hunting down an external tape player with the same connectors, I finally figured it out. The power is cut to the “front” part of the radio and power is fed into the “back” of the radio along with an audio source. Add some simple swtiches and you have a 30-year-old iPod-compatible stock Datsun radio. Cool. I made a few and posted the information on the Datsun roadster website.

A quick sketch

A quick sketch

I’ve long been a fan of mid-century modern furniture and design. I have collected quite a few images of radios and audio equipment from the “jet age”. Somehow I got to thinking about making miniature console stereos. With vintage car radios. And why not use automotive switches for the controls? And car badges for the brightwork. I started making sketches on paper as well as in Paper (the app).

Amanda had an Ikea drawer box that belonged to her mother. It sat on the table in the garage and I must have looked at it a hundred times before I realized it was the perfect size to house a radio, a couple of speakers and a power supply. I wish that Ikea still sold these!

Simple radio sketch

Simple radio sketch.


Legs and square speaker grilles? Looks like it escaped from Pee Wee’s Playhouse!


Wrinkle finish face and red, green and blue input switches.

It seems that a lot of people are interested in adding bluetooth input to vintage radios and I did some investigation and found some great little bluetooth receiver boards. Then I started researching ways to switch the inputs – yes, you could just use a series of switches to select between radio, line-in and bluetooth sources, but it was clunky and it had to be done just right and in the proper sequence – not very elegant. I finally found an approach that used momentrary switches and a matrix of diodes to trigger latching relays to select the source. The relays I use come from only one place – a a guy on ebay from England who sells vintage 12 volt 4-pole-double-throw latching relays. This is the “brains” of the Shift-Tone radio.


Version 1 of the “brains” – using automotive relays made them too big for the case.

To do all of this testing and experimentation i needed a source of 13.5 volt power (your car’s 12 volt system really runs at 13.5 volts). I found a bench supply at a Surplus Gizmos, then found a vintage Heathkit power supply at a garage sale just a block from home! I searched and searched for a cheaper supply and finally found a source.


Version 2 fits underneath the radio. Testing the wireless with some Wire 154.

And so all the bit and pieces came together to make a “proof-of-concept” test mule. Using the Ikea box saved lots of time and bother and let me concentrate on the electronics.


Works great!

All-in-all the little purple radio works great! The switches select between the radio, line-in and bluetooth sources. New Dual 5.25″ speakers sound pretty good.

It took just about a year to go from the idea to the first version. The power supply and switching system took quite a bit of head scratching. In the mean time, I’ve made sketches of many variations and some of them have some really wacky ideas! The second radio will be written up soon – the Volvo DeLuxe.




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