Building the QRPguys Multi-Z tuner kit

Building this kit was good exercise; if it works properly when I try it out in the field it will be entirely due to the truly excellent and detailed instructions that I downloaded and printed from the QRPguys website! Get ready for lots of pictures and discussion as we go through the process!

The whole tuner is built on a “chassis” assembled around the main circuit board, with a front panel and its two supporting gussets. All of them have strategically placed solder pads to hold them together. Here is the first place where the instructions really shine; they explain in detail precisely how to achieve a perfect result.

Using this improvised block and a piece of tape, I was able to position the main board and front panel slightly out-of-square so that they were perfectly square when the solder cooled and shrank.
With the front panel properly placed and aligned, the gussets were easy!

Placing the through-hole components was also simple and easy; but then came The Winding of the Toroids … the little one was not so bad, 25 turns, one tap. Again, the detailed instructions were crucial to my success. For the common case of losing count somewhere in the middle, they advise taking a photograph and viewing it enlarged on a screen, and this did in fact make for an easy recovery when I lost count!

Next, tinning the leads for soldering! This proved difficult with my tiny 15 watt iron, so I had to get out one of the big ones!
95 watts, made for the Bell System by General Electric, it might already be as old as I am, and it looks to be good for another century or so!
The finished product.

Now for a few more components, like the variable capacitors and BNC connectors, two of each. Not shown, the captive stainless steel wingnuts for connecting wire or balanced line.

I was also impressed with the thoughtful design, as shown by the perfect fit of the parts. The variable caps shown here are an example of that.
Ever since I got the bag full of parts I had idly wondered how they got the conventional-looking knobs on the little stub shafts of the variable caps … when I got to this step, all was made clear! A short nylon spacer and a metric screw made a neat shaft extension! Pro tip, not in the instructions: use your thinnest needle-nose pliers to grip the flats on the brass stub shaft when tightening that long screw.

Which brings us to the last (but definitely not least) part: winding and installing the big toroidal transformer. Getting this crucial part right absolutely required every bit of the detailed instructions!

Preparing the center tap of the main winding from 2 measured lengths of wire.
A pair of chain-nose pliers really helps to form the loop.
Loop closed and soldered; ready to start winding!

Doing the three windings correctly (using measured lengths of wire, all wound in the same direction from a center point) really required all of my attention and I took no pictures of intermediate stages as a result of that focus.

The finished transformer; note the labels to keep track of the multiple windings
A lot of careful scraping with a small knife got the enamel off the wires. To be certain that the right wire went in the right hole for soldering, I inserted only a few at the start.
Then I fished the remainder through one at a time, not removing the labels until the last moment.

And when I clipped off the excess length of the last soldered lead, it was done. A gentle bath with rubbing alcohol and a toothbrush to remove rosin flux, stick on the 4 little rubber feet, and it’s ready to go!

Coming soon, build reports on the other two kits, and then some evaluation on the bench and in the field. Thanks for coming to driftlessqrp to read this, I hope you will come back for more!



, ,




Leave a Reply

Your email address will not be published. Required fields are marked *