Wednesday, October 21, 2009
More 1928 Hartley
After a little debugging it works!
When I first put power to my version of Ross Hull's Hartley transmitter I could only get it to oscillate if the cathode clip is either not attached at all or clipped to the tank coil near the plate (rather than grid) end. RF with the clip this high on the tank coil is detectable on a nearby receiver but not measurable at the transmitter antenna.
It turned out that all things that look like RF chokes don't make good RF chokes. Mine from my junque box looked like a single layer vintage RF choke, it tested good for continuity and B+ showed up at the tube socket but didn't work well in this circuit. Replacing it with a
more modern RF choke fixed my problem. I'll need to go back and hand wind one like shown in the original 1928 QST article.
I also needed a 4:1 balun to match well to a 50 ohm load.
Now with 300 V B+ and about 25mA input I can push it to over three watts out. Backing off gives me a clean 2 watts out.
Thank you to several AWA friends that helped with parts and advice.