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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