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Author Topic: MFJ Cub 9340 - low ouput  (Read 5630 times)
AE7UT
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Posts: 72




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« on: August 27, 2014, 12:59:47 PM »

I just finished my 9340 cub.   It was fun and I made 2 QSOs last night.
It seems to be working fine.....but.
I'm only getting 1.3 watts out.  It seems like the output really varies between
builders and kits.   Should I replace the PA transistor?  What has been your
experience with this and what would you suggest.

73
Stan AE7UT
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N2DAY
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Posts: 1




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« Reply #1 on: August 27, 2014, 05:25:02 PM »

I have the 20 Meter Band cub and have about 1and half output so I think yours is about right. With these low output rigs its hard to read accurate watts out on most watt meters. As long your making contacts I think your OK
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W4OP
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« Reply #2 on: August 27, 2014, 08:18:04 PM »

So you are about 1.9dB low. How are you measuring power?

Dale W4OP
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AE7UT
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Posts: 72




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« Reply #3 on: August 27, 2014, 10:23:36 PM »

I'm using a Ten Tec QRP watt meter I built last year. 
It seems pretty accurate when comparing the output from my other QRP rigs.
Thanks for the replies.
73
Stan
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W1JKA
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Posts: 1767




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« Reply #4 on: August 28, 2014, 10:18:56 AM »

Re: AE7UT

  As previously mentioned 1.5w is about average for a 12v battery supply, I run my 3 Cubs off auto jump start batteries 95% of the time, however I do get a solid 2w when running them off my home 13.8 v PS. You're correct , output will vary between builders and initial tune up experience and test equipment availability. I wouldn't change the PA, at the most all I would do is a quick hit on all solder connections again and check for any minute bridges.
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W4OP
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« Reply #5 on: August 28, 2014, 10:34:59 AM »

Hi Stan,
I can't find a QRP  wattmeter on the TT site.  The Bird 43 meter is accurate (from memory) to +/- 5% of full scale. So if we assume the TT meter is that accurate (unlikely) and your full scale is 10W (?), then any reading taken would be accurate to+/-0.5W. If FS is 20W then +/-1W etc.

Dale W4OP
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AE7UT
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« Reply #6 on: August 29, 2014, 01:30:51 PM »

The watt meter is a Ten-Tec 1225.
It's a great kit by the way.   One of the first I built to hone my skills before attempting the K1 and K2.

OK... strange as it may seem.  I went home and put the lid on the kit and tested it again tonight.  I got a hint from a guy on the MFJ board.   He told me to try spreading or pushing the toroid coils.   It seemed to work even though I didn't move them by much.  I'm now getting 2 watts out from my 13.8V power supply.

I'm happy with that.   

Thanks for the help guys.
I hope to hear you on the bands.
If you hear a weak signal coming out of Utah... say hi!

73
Stan AE7UT

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W4OP
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« Reply #7 on: August 29, 2014, 04:09:12 PM »

Great work Stan- hope to hear you on 40M,

Dale W4OP
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