To: <amps@contesting.com>
> Date: Mon, 25 May 1998 10:19:02 -0500
> Yesterday I did some additional experiments on my amp. I put in a
> different tube that I had gotten from someone and this tube had a lot
> more gain. On 10 meters I was now able to put out at least 1200 watts
> with AG6K's supressors. However, I decided to do the ol' stability check
> on the amp with this tube. Guess, what, with my tune C at a minimum the
> amp began to take off. The added gain of the tube was enough to make it
> happen.
Woops. The shotgun missed the target. Saw the barrel off and shoot
again.
> And when I added the cover to the amp, it would fly even easier.
> I tried a couple of other things, but to no avail. Finally, I added a
> third AG6K RL supressor in the anode line (just experimenting). This
> took care of the oscillation. And I was down to about 1150 Watts now.
Ahh, you cut the barrel off.
> So then I went to 15 meters. Some odd things began happening. The load
> C started popping and arcing. And the caps position changed as well. It
> had been tuning up good with the cap at about 1/3 of maximum. Now it
> wanted to tune up with the cap fully meshed. Previously the fully meshed
> position was a false tune point. And still all kinds of sputtering. I
> could move the cap just a hair and lose all output power. Strange
> behavior.
Yes, especially since Rich claims parasitics cause this type of
effect. That's why I remove, on average, about ten AG6K kits a year
from PA's.
> Then I put the lid on and all heck broke loose. I keyed up and *BANG* it
> went. As I said before, I've been using AG6K's suppressor ideas. He
> suggests a 0.5 Ohm combination of resistors after the plate RFC. These
> resistors are what went bang. I also blew 2 10 watt 10 Ohm current
> limiting resistors (in series) on the supply side of the plate RFC. So
> something REALLY happened yesterday.
Gassy tube Jon, or a series resonant choke or leaky coupling/bypass
cap at the anode. Change the bad part instead of waving batwings at
it.
> So I am looking for suggestions from anyone. Perhaps I have a layout
> problem. I seem to have a cabinet resonance problem, etc.
Maybe a ground loop or unwanted tank or choke resonance affected by
the cover, but absolutely not a "cabinet resonance" problem unless
you have a ten foot long chassis.
73, Tom W8JI
w8ji.tom@MCIONE.com
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