I would have never left it running for that long. This amp was only designed
for 50 watts out. You probably overheated the cavity and after you left it off
and it cooled down it now is making contact in the cavity. In my experience
with these amps, leave the 8930 in place. You said you only wanted 150 watts.
Did you note the difference in anode size when you changed the tube? 350 watts
output is about the safe max on SSB. I know you here about 500 watts out, I can
guarantee not for long, and it will sound terrible. I modified my last one by
cutting the power supply away from the cavity and making it 2 pieces. Much
easier to transport to mountain tops, and you can replace the noise maker 400hz
fan with a bigger ac fan for more cooling.
But again opinions are like a## H#### every one has one.
K6KWQ Dick "12 Volt radios are for wimps, real radios can kill you" Still can't
make it go QRO with "More Power"
----- Original Message -----
From: Web Williams
To: amps@contesting.com
Sent: Sunday, September 12, 2004 10:58 AM
Subject: [Amps] AM-6154 questions
I thought I'd come in here begging for an answer, since I have not
been able to turn up anything on the internet about an AM-6154
VHF amplifier that I have.
It's been working fine with an 8930 for about three years, but
seeing all the improvements being raved about, I felt compelled
to try a Svetlana 4CX-400. The tube swap was uneventful, as
well as the tuneup with the new tube. Everything looked just
fine! I was advised by the tube seller to "keep it down" for the
first 24 hours or so, and he provided me with a procecure for
tube burn-in. I had no way to do it the way he described, but
he said alternately that I could leave the amp turned on for 24
hours, and if there were any problems with the tube being gassy,
or having a bad seal, it would likely show up.
After checking for output (I did want to see if it was going to work)
I tuned up at about 150 watts for a couple of watts in, and everything
looked great! I assumed (hope I was correct) that this minimal power
level would not really stress anything. I then left the amp turned on for
24 hours to burn in.
The next morning, I went to my shack, and checked everything, and it
seemed just fine. Same 150 watts output (I had not tried to go for max
smoke yet- I have an ARR preamp in line that is only rated for 160 watts
pass-through). I heard a station on, and called him. My wattmeter is
situated where I cannot see it when I am speaking into the microphone.
After several unsuccessful calls, I looked over at the meter, and it was
dead on zero when I was transmitting!
I made an assumption that I blew the new tube, so I quickly put the
8930 back in. Still no output (after retuning to proper positions on all
dials).
Both fuses on the front check good with my DVM. Plate voltage goes
to mid-scale (not sure how this unit was set up, I didn't do it, and don't
know who did). Screen voltage is 40 (about 3/4 scale) and grid voltage
goes to 50 (not pegging the meter, but almost). Heater voltage puts the
meter at 28. Still no output!
I let the amp sit for about a week, went back to it, and still no output.
Three weeks of sitting there without me even touching any controls
I went back to it, and it's fine! Other than turning it on and checking the
voltages by spinning the test switch through the various test positions, it
seems perfectly OK! (Didn't put the 4CX400 back in it.)
Does anyone have any ideas as to what to check? I'm totally lost!!!
Thanks, -Web Williams in Myrtle Beach, SC
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