Radio Bench Fun!
Every once in awhile I’m reminded of the magic of radio and why this hobby is so much fun!
For the past week and a bit, in between power outages of up to four days, I’ve been optimizing a circuit from the December ‘36 ‘Radio’ magazine.
It looked like it might be something that would be fun to use during the weeknight NRN (Novice Rig Nights) activities ... a Jone’s-style push-pull crystal power oscillator using a pair of 6V6s. The original article called for 6L6s but my power supply can probably not provide much more power than is already coming from the 6V6s and these will likely be easier on my few precious novice-band crystals.
The circuit is lashed-up on my very well-worn 'aluminum breadboard', which is peppered with numerous convenient holes punched or drilled for mounting various crystal sockets, tube / coil sockets, variable caps etc ... it really looks awful but allows easy parts swapping to test out different configurations.
This afternoon I had the thing perking to my satisfaction, along with a very sweet-sounding CW note, using my WWII - era 7121kc crystal. Everything looked good into the dummy load so I connected the 40m antenna through the tuner, clipped the bug to the cathode resistor and at about 40 minutes before sunset, sent a short ‘CQ’, hoping for a nearby local but not really expecting a reply ... now this is the magic part.
My CQ was immediately pounced-upon by John, N2BE, on the other side of the continent, in New Jersey! I shook my head at the dangling pile of clip leads and just-barely soldered components clamped in the bench vice and had to smile when he gave me a 589 report! John was working the AWA's Linc Cundall CW Contest, where rigs must be pre-1950 designs or builds. I was happily able to give him a legitimate point, using my 1936 Jones oscillator!
At 400V on the plates, the little lash-up puts out 18 watts and seems to be about 45% efficient ... not too bad for a power oscillator. As well, the crystal current must be low as it keys nicely and doesn't sound stressed.
I’ll soon be rebuilding the little transmitter into something more presentable, probably similar to my Tri-Tet-Ten, using the short-lived but visually attractive mid-30’s building style that mated a shiny aluminum plate to a nice wooden base.
Stay tuned ... I’ll hopefully have it completed over the next few weeks and will be looking for some 80 / 40m NRN Monday night fun!
Why the suppressor coil only on one plate?
“see text” is in the original article, of course.
Now I have to check my old stock of Radio to see
if I have that issue..
Perry, apparently the original build suffered from a UHF parasitic oscillation which the 8T choke effectively eliminated. It was not necessary to insert it in both plate leads it seems. I’ve noted no parasitic or instability so have eliminated it.