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   Home   Help Search  
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Author Topic: Power out increases until the load cap is 100 % meshed  (Read 13361 times)
KM4AH
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Posts: 945




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« Reply #45 on: February 13, 2018, 03:38:15 AM »

When we get older, we take shortcuts and at times miss simple things while working/ troubleshooting circuits.
One big one that got me a couple of times is that I could not measure voltage in a circuit, and started tracing backwards and found I did not have power hooked up to the circuit even though the power supply was turned on.
Another problem is changing out parts and finding out the load was wrong.
I just bet a dummy load was not used to isolate the antenna system. I also expect the use of a  antenna analyzer was overlooked.
Changing out parts needlessly is a bummer if you overlook the obvious. 

It sure is good you checked in. None of us would have ever thought of that.
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W1QJ
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Posts: 2947




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« Reply #46 on: February 13, 2018, 05:18:40 AM »

I think all hams should read a generic "troubleshooting" book.  Better yet, if you are working on amplifiers perhaps reading a book on basic "amplifier troubleshooting" is more appropriate.  I honestly don't suspect that we should have to ask the question to someone seeking the help of the group if he has his amp plugged in or if he has his coax cables switched or even if he has a bad jumper coax cable.  Basic bare bones troubleshooting should go a long way and catch 50% of the simple fixes that come down the pike. 

I would also suggest in the case where a ham will be doing several upgrades to a vintage amplifier like an SB-220 or an SB-200 or whatever, that if they are not seasoned at doing such work on amps that they only complete on upgrade at a time and after each one go back and make sure that the mod they just did works and the amp functions properly before moving on to the next one.

All too many times someone will come along and says, I installed all the Harbach mods on my amp and now the amp does not show any HV and the amp will not keep into transmit and there is no reading on the HV meter  and when I switch to grid the meter goes negative and the meter lights are very dim.  That would seem to indicate that just about every mod done has a problem with it.  This person will spend a month getting his amp straightened himself, even if he does.  One mod at a time and check progress after each one.

Because I have been doing these mods for 40+ years I can go through all of them without instructions and complete them all at one time and when finished turn the amp on and go.  I could not do that in the beginning but at some point I was able to.  Do one at a time and make sure you are good before you move on.

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W8JX
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Posts: 13268




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« Reply #47 on: February 13, 2018, 05:46:36 AM »


One mod at a time and check progress after each one. 

Do one at a time and make sure you are good before you move on.


Very good advise
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--------------------------------------
Ham since 1969....  Old School 20wpm REAL Extra Class..
KM4AH
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Posts: 945




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« Reply #48 on: February 13, 2018, 01:43:00 PM »

With this amp the guy took a no tune amp which basically has a C1 and C2 for each band padded appropriately for space considerations and converted it to a standard tune. It really didn't matter where the 500 and 750 were for 75 meters because they were added. It worked better with the 750 on the 40 meter band switch position instead of the other way around.

Now, could you change it to an air variable with more range ?  Of course.  But, it is not my amp, I won't charge anything , and it loads pretty much in the middle of the range on 40 and 75 didn't change to amount to anything.
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W1BR
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« Reply #49 on: February 13, 2018, 01:56:17 PM »

Without knowing the grid current readings  and just how heavily loaded the amp really is this is all idle speculation...
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KM4AH
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Posts: 945




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« Reply #50 on: February 13, 2018, 03:33:55 PM »

Without knowing the grid current readings  and just how heavily loaded the amp really is this is all idle speculation...


The amp would not tune to peak output with an appropriate conservative drive for 2 3-500Z's  without running out of the range of C2 .

If you can't tune to peak output I'm not sure how you know where to tweak the load for grid current.
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W4BOH
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Posts: 10




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« Reply #51 on: February 24, 2018, 04:32:42 PM »

What is Z of antenna?
If it's quite low, you'll need more load cap.
What does the amp do into a dummy load?
Low Z loads take a LOT of loading cap to match properly.
Wilson
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