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   Home   Help Search  
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Author Topic: 811 hxce  (Read 5976 times)
SA4MDN
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« on: December 08, 2013, 04:30:28 AM »

once the amp is tuned it works fine, when I go to use it again after being in standby for a while it needs retuning again by quite a bit, then all is fine until its used again after being in standby, this is on all bands that it happens, does the same thing on either of my antennas and dummy load, and with or without alc set up, it never used to do this, I could come back to it after not using it for a day or so and it never needed retuning. all meters read fine when tuned up, any idea's what's going on, thanks
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W1QJ
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« Reply #1 on: December 08, 2013, 05:31:49 AM »

Have you tried changing the blocking capacitor?
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SA4MDN
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« Reply #2 on: December 08, 2013, 06:37:28 AM »

still under warranty so not sure on playing around inside just yet, if its just one of those things I can live with it, but if sounds like something has popped inside i would like to get it fixed before the warranty runs out in a few weeks,  never been inside an amp and not so sure I would know what to look for even if I did.
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W1QJ
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« Reply #3 on: December 08, 2013, 07:37:19 AM »

I am almost certain that might be the problem and if it is, it is an easy fix.  It is something you can easily do yourself if you can solder.  Would save a lot of headache for everyone if you can change that part yourself.  Very simple fix.
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SA4MDN
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« Reply #4 on: December 08, 2013, 09:38:40 AM »

thanks for your help here W1QJ, excuse my lack of knowledge here but what does this blocking capacitor do, any idea where in the amp it is and what it looks like,, also can it be tested.
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W1QJ
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« Reply #5 on: December 08, 2013, 10:45:43 AM »

The blocking capacitors (2) are located in between the RF coil PC board and the parasitic suppressor board.  They are (2) ceramic disc 1000pf caps in parallel.  They are a yellow color and are side by side one another.  I predict that one of them may be flaky.  There really is no way to test them.  You could test them with a meter to see what the capacitance is but that won't tell you anything about how it behaves when RF current is flowing through it.  One of them may be flaky.  If you are lucky maybe only one is bad and if you remove one and check for your problem on 20 meters into a dummy load and see if it goes away.  if it doesn't then connect that one again and disconnect the other one and check again.  The amp will operate just fine with one of those caps on 80 meters and above.  There are 2 of them for 160 meters.  You can do this test to see if this is your problem.  If it is not than you can eliminate that as the culprit.  You won't need any parts to perform the test to see.  On the other hand your problem can also bee an RF connection somewhere that is common to all bands/  You would have to carefully inspect every RF connection in the tank circuit and through to the output SO-239.  A poor connection can easily cause the problem you are having.  So I think it is something you can find out for yourself.  You won't void the warranty by just looking for a poor connection and correcting one if you find it.  If it turns out to be a blocking cap you can order 2 new ones and install them yourself if you know how to solder.  Of course make certain the amp is unplugged and the caps bleed down before you go inside.
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SA4MDN
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« Reply #6 on: December 08, 2013, 10:57:12 AM »

ok thanks for that, I got 2 weeks off over Christmas will have a poke around in there then, one thing I forgot to mention is that its taking a lot more load to tune it up now than it did before, where it used to be about 2/3 load for 3.789 its now 5/6, no change in plate setting, don't know if that narrows down things a bit more
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W1QJ
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« Reply #7 on: December 08, 2013, 11:17:39 AM »

I have run into just about every problem imaginable with amplifiers.  Usually when an amplifier presents the problem you are seeing, it is usually a part the is getting affected by a heat change.  Either that or it is a poor connection like a cold solder connection on an RF junction.  The fact that the problem persists on all bands indicates it is in a section of the amp that is common to all bands.  This means all RF junctions and connections common from the input of the amp to the output.  You can't overlook the fact that you may even have a bad coax jumper cable someplace external to the amp.
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SA4MDN
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« Reply #8 on: December 08, 2013, 11:23:10 AM »

ok thanks again, will have a swap around with the jumpers first as that's the easiest, and then delve deeper over the holiday if no change with different coax cables
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W1QJ
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« Reply #9 on: December 08, 2013, 11:38:06 AM »

OK,  please do come back and report your findings,  the group is always interested in knowing what the outcome was with problems brought here.  I bugs us when we don't hear back form folks who have presented us with problems and we try go help.  Good luck and hope to hear that your amp has been fixed and what the cause was.  Lou W1QJ
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SA4MDN
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« Reply #10 on: December 08, 2013, 12:08:00 PM »

ok will do, just swapped out all my coax jumpers with new ones and run tests through all the bands into a dummy load, all seems to be fine now with no retuning after being in standby, but I still have the higher load setting than I used to have but looks like its only on 80mtrs from what I've seen so far. so looks like I maybe had 2 problems going on here with one now sorted. 
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W1QJ
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« Reply #11 on: December 08, 2013, 12:13:35 PM »

All sorts of things can have an effect on loading.  If the amp loads normally and it does not change afterwards, I would not worry about the fact that you have a different setting.  It looks like your problem was a poor jumper cable.  Get rid of the bad one and throw it in the trash so you don't use it some day and find yourself with  a problem due to it.  Now you can have have a happy Christmas knowing your amp is good to go again.
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SA4MDN
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« Reply #12 on: December 08, 2013, 12:22:34 PM »

cant thank you enough for you help with this tonight, im a happy bunny again with a relaxed Christmas ahead, know its a bit early but have a good Christmas and thanks again, Michael.
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