Many, many years ago when I was a teenage geek, I was green with envy at the Coil Winding Calculator that an older friend had access to in his university lab. It was an extremely useful device – a cardboard slide chart that allowed you to compute the parameters for winding a coil of a given inductance (trust me, when you homebrew your own ham radio gear, that’s something you really need to do).

So, I went and reverse engineered the thing and cloned it with a Xerox copier and some cardboard and glue. I ended up with a device that was far uglier (in those days copier technology was still pretty poor) but it worked just like the original. It served me for years, then went into my computing device collection. Over the years I forgot the original completely, to the point that I had no idea what color it had been before I recreated it in smudged gray…

So a few weeks ago I had a stroke of serendipity when I ran into the “Allied RF Resonance and Coil Winding Calculator” in the Vintage Instruments online store of Dick Rose – it was the same device! Dick shipped it over, and now I remember: it was indeed orange in color. So now I have the two devices in my collection, side by side; and here you can see them in the photo. Not that I wind any coils these days (though I’m still a happy geek), but it’s nice  to close a loop across the decades and finally have the original device I so coveted back then…

Allied Coil Winding Calculator slide charts

For the full story on the Xeroxed calculator, see here.