QCX 30 (rev. 3) revived!


Hi Hans and group,

In 2018 I bought a QCX 30 (rev. 3 kit). Couldn't QSO in morse then. My excuse for buying it, was to start learning morse code. I ended up not using it much, because well, learning morse code takes time and dedication. A year later I took the CWops Beginners and Basic course, and now I can (as a newbie) do morse code. In the mean time I have built other QRP-Labs kits which are fun to build and work great!

So last week I picked up the QCX 30 from the diplay cabinet. But found out it's transmit output power was low, even at 15V. During key down the power slowly rose from 1.5 to 2W. The manual and posts in this group were a great resource in finding the problem!

First I counted all the toroid windings and guess what... T1 was OK, but L1, L2, L3 and L4 all had an extra turn! Thought I was a bit of a perfectionist haha, but no. Thinking I had resolved the problem in removing a turn, I connected the QCX and tested the output power. Unfortunately still about the same low power output and slowly rising, this time maybe to 2.3W at 15V.

One thing I read in this group was to check C25 and C26 (560pF for 30m LPF). They were getting hot during key down. Temperature rose to about 60C (140F). So they were my next target. I replaced the caps and now the power output was between 3.5 and 4W depending on where/how I measured.

Still not completely satisfied, I ordered the Peak LCR45 meter to be able to measure the inductance and capacitance. One of the old 560pF capacitors was measuring 475pF and the other 22pF. So I definitely messed them up in the past! Then I found out that the L1 and L3 inductance was a little bit higher than specified in the documentation. I removed 1 turn from both and that together with the new caps was the solution!

Power output measured at 15V (with D3 in place) is 4.8W, at 12V this is 3W. So I'm really happy with this revived QCX 30! In the mean time I also did the keying envelope mod and next up is a nice case and making some QSO's!

So thank you Hans for the great kits, documentation and info on your website, also to everyone in this group for discussing and finding solutions. I can learn so much more from you all, I'm hooked and I will continue to build your nice kits! Who knows I might end up with an oscilloscope or spectrum analyzer.

73, Ben


And here it is :)