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Author Topic: Ameritron 811 has low output on 80 and 40 but does great on 20 and above???  (Read 1042 times)
KI4EU
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Posts: 11




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« on: November 06, 2017, 06:05:06 PM »

I have this used 811 I bought a few months ago and never got around to checking out until today.
I tuned it up per instructions to about 450 watts on 20M and got a return call on my first call with it with good report.

Later I decided to try it on 40 meters, only to learn that it will only do about 150 watts!  So not having an 80 meter antenna, I used a dummy load and tried it on both 40 and 80 and got the same results...poor output.  I was under the impression that failing tubes would show more at higher frequencies, but this one will do 400 watts on 10 meters and only 150 on 80 or 40.

I was driving it with an old IC-740 which runs full output barefoot, but used about 70 watts today with the amp.  On the lower bands, no increase in output from the amp with greater input than 70 watts.

I have a schematic but it is very blah compared to the ones I have been using on Icom rigs.

any ideas?
Thanks. Win, KI4EU
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N5RMS
Member

Posts: 54




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« Reply #1 on: November 06, 2017, 09:00:53 PM »

Have you tried loading into a 50 ohm dummy load?

Allen
N5RMS
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N3QE
Member

Posts: 4883




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« Reply #2 on: November 07, 2017, 06:02:40 AM »

If you aren't even developing much plate current on 40M/80M, the problem could be switch wafer alignment. Here's how to check: https://www.w8ji.com/al811_input_switch_alignment.htm

If you are getting a lot of plate current draw on 40M/80M but not developing much output, then the place to look at is the switch wafers and pi-network components near the front of the amp. If one or more of the padding capacitors have gone open it might feel like "I can't turn the plate or loading control far enough to peak it up". But it's also possibly just a switch wafer.

« Last Edit: November 07, 2017, 06:09:23 AM by N3QE » Logged
KM1H
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Posts: 2502




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« Reply #3 on: November 07, 2017, 07:16:31 AM »

Quote
Have you tried loading into a 50 ohm dummy load?

Allen
N5RMS

Did you actually read that first post???
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W1QJ
Member

Posts: 2606




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« Reply #4 on: November 07, 2017, 01:02:09 PM »

I'll bet any money that his power reading device is out to lunch!
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KI4EU
Member

Posts: 11




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« Reply #5 on: November 07, 2017, 05:50:24 PM »

Lou, you are very good.  Next time I have a problem, I will email your directly!  HI HI.
You are correct.  Bad power meter.  First I thought it might be the transceiver, so I disabled the amp and found the same result.  Then I switched the power meter to another one and sure enough, getting 600 watts out on all bands!
I really appreciate the comments.  When  you talk about an issue you are having, it's sort of like looking at yourself in a mirror, ideas pop out.
73!
Win, KI4EU
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W1QJ
Member

Posts: 2606




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« Reply #6 on: November 08, 2017, 03:18:11 AM »

Win, there’s a big difference between a power meter and a true watt meter.  I use the terms very carefully.  I’ve been using a Post LP-100a for quite a while now and find it quite accurate.  Improper readings will drive you nuts as it did to you.  Unfortunately it’s an assumption that many of us who hang here make, that when someone comes in for help they really have a problem.

I know a guy who tore his pump apart because he had an input matching problem, after days it was tracked down to a bad jumper coax.  This is when proper troubleshooting techniques come into play.  Some years ago I taught “troubleshooting 101” if you will yo industrial students.  I always got good laughs when I started out by saying to check if the damn thing is plugged in!

I’m glad your problem was simple and solved.  I shared a repair I did the other day on sn amp with another ham and when I told him what the problem turned out to be he said he’d of never thought of checking that in a million years.  Troubleshooting is an art as well as a science and you need both skills to be really successful.
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W1NK
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Posts: 606


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« Reply #7 on: November 08, 2017, 06:39:09 AM »

Whether troubleshooting or making a diagnosis ....

When you hear hoofbeats, don't look for zebras!   Wink

Frank, W1NK
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