Hi Art (and others),
I thought I had been hitting "reply" to the list, but apparently my replies
are only going to the person who posted back to me on the list.
No, I did not let the amp operate key-down for 24 hours. I only had
filament voltage, screen voltage, and grid voltage on. I didn't turn the
plate voltage on. I have no way to turn off screen and grid voltage, or
at least, there is no switch on the front to control that, just a switch
for
the indicator meter that provides "relative" readings of voltage being
present.
I'm fairly positive that my problem is an intermittent connection
-somewhere-,
at this point, since just hanging around and waiting about three weeks made
the amp work again. I did absolutely nothing to effect a repair, it just
started
working again on it's own. I will probably run it every day for a couple of
weeks for a short time to see if it's really "fixed itself" (not likely)
and if it
keeps running, will swap the tube back out again and see what happens.
This has happened before- about a year ago, and I heard a spark crackle
inside the amp and it immediately begain working again, and never stumbled
for the entire June 2003 VHF contest! (Like I said, it's been awhile
since it
bombed out...)
I know some guys who work on things for years and never find an
intermittent
problem, but I thought since I had not tried this list before, and the
real Guru's
seem to hang out here, that perhaps someone else may have had a similar
experience and effected a cure. You never know until you ask, right?
Next time it flubs up, I'm going to write down the readings at each switch
position on the meter. This problem occurs extremely infrequently and
usually
at the worst possible moment for it to happen!!!
I will (hopefully) get to swap out all the jumpers in my shack over the
next
two weeks. They're all a mish-mosh of different brands and grades of coax,
and I got a deal on 200 feet of silver-teflon double-shielded stuff.
Could be
a bad jumper all along.... and I have been using UHF-to-N adapters on the
back of the amp. I hope to have "real" N jumpers....
Thanks, -Web Williams in Myrtle Beach, SC
KY1K wrote:
I read the original post again. When I read it originally, I never
thought he turned it on and let it cook at 150 watts over night. But,
maybe that is what he did.
I hope to run one of these someday and have an interest in digital
modes (which means running key down for 30 seconds to 2.5 minutes). If
I upgrade to the bigger tube, will these amps run keydown for long
periods (limited by the tube) or does the power supply/cavity give up
first?
In previous discussions of these amps, I've never heard anyone who
used them complain about not being able to run key down for extended
periods.
Thanks all.
Art, KY1K.
At 03:17 PM 9/12/2004, you wrote:
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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