[AMPS] More amplifier experiments

Tom Rauch w8ji.tom@MCIONE.com
Mon, 25 May 1998 17:49:18 +0000

> 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 
> 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 

> 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

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