Viking II 20 meter problem, again

[WA2ROC]

last night on the 20 meter AM net, my Viking II was operating just fine.

Then, all of a sudden, as I was spotting the VFO on frequency, I heard a loud hum from the receiver rather than the heterodoxy from the VFO and the received signal. When I called the station on frequency, he responded that my signal was quite a bit weaker than before.  I looked at the power meter and sure enough, it read about 45 watts out, rather than the 100 watts that were there before.

The plate current was down also, but I was able to increase loading and get the Ip back to about 200 ma, but still only 45 to 50 watts out.

I politely signed out, set the band switch to 40 meters and got a booming 100 watts out.  Back on 20 meters, grid drive was fine, but still not normal power output.

Today, I will swap out the 2 6146's and hope for the best.  If not, off the desk it comes and over to the work bench to look around inside, voltmeter in one hand and the other hand in my pocket.

Anybody have any good starting places?

[w4bfs]

log your power out vs plate current into 50 ohm load for each band ....plate and load settings as well .... note any instability

[WA2ROC]

Got a chance to look at the Viking II last night.  Opened the top and checked out the band switch and contacts.  All looked clean and bright, no loose wires.

Powered up the rig and tuned it up on 40 meters.  100 watts out into dummy load.  Went to 20 meters, 45 watts out.

Pulled the 6146's out and replaced them with a known good set.  Re-tuned on 20 meters and voila 100 watts out into dummy load.

Then I checked the control settings.  I believe I had the oscillator and buffer tuned at a different place than before.  Maybe even the final tank, which if set wrong, can make the finals work like a doubler. Shoulda written the original settings down, but didn't.

Anyway, I put the original 6146's back in, and there was 100 watts out on 20 and 15, maybe 80 on 10 meters.  160, 80 and 40 also good power.

I wrote down the control settings for future reference and a starting point.

Pilot error, needless to say.