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| 1935 ARRL Handbook. Source: http://www.arrl.org/ |
John and I had a nice QSO today on
80m CW and the rig sounds just great. He reports 240 volts on the
plates and a current of 58ma. His scope-measured output is just over 8 watts for
an impressive efficiency of just over 60%. It appears that the Colpitts-style is
much more efficient than the more popular TNT or Hartley oscillators...well at
least more efficient than the ones I built!
Although John did not have every period-appropriate component available to him, it didn't discourage him from building his BK rig. For too many, this is often a stumbling block that leads to nothing being built....as the boy's of '29 no doubt would have done, he put something together completely from his junkbox.
It will be super to have another left-coast station in this years '29 Party...and a Canadian station to boot!
Anyone else building for the BK? ....there's still a few weeks left.
4 comments:
After seeing Steve's previous blog about the Bruce Kelley QSO party
and the type of transmitters that other amateurs have built.
So I looked in my old tube box in my workshop attic and found
I had a couple of 45 tubes.. then checked my tube socket box
and found a couple of old four pin isolantite type tube sockets. Wow.
I could put together such a transmitter. More searching
and found more parts.. Hey, I'm good to go..
After throwing things together and trying various push-pull
circuits TNT, TPTG and finally settling on the Colpitts circuit
that seemed to work really well right of the bat.
Maybe it won't pass muster for the purists out there. But after several
QSO's with it on the 80m band, I hope to have a few contacts in the
Bruce Kelley QSO party.
Your Colpitts is performing extremely well I think. I'm sure that it probably wasn't popular back in the day because of the much higher parts-count, which evidently pays off in performance. You will be amongst a select few in the BK using a Colpitts!
How is the antenna/load coupled to the tank coil? 60% is really impressive. I struggle to get 15-20% efficiency with my Hull Hartley.
Just confirming today on my measurements into a different 50 ohm load gives 60v peak to peak sine wave or 9watts.
Using two turns the same diameter as the tank coil #14 insulated wire at the center of the tank circuit about 3/4 way into the winding. Now to try for 160 meters.
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