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KL-503 help needed Not the KL-503HD

FlyBoy50

FlyBoy50

Sr. Member
Feb 22, 2019
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I hope this is posted OK because I'm using it on 11 meter. I've been having some trouble lately talking DX and I'm beginning to suspect my KL-503 amp because it trips the SWR warning message on my Q6 Pro when the amp is turned on. If the amp is off I have a 1.1-1. In another thread someone mentioned tuning or modding a amp so it doesn't raise the SWR when put in line. I'm wondering if that can be done with a KL-503 or is there No Such Luck on a cheap KL amp. I wish I would have heard about the KL-503 HD before I bought the plain KL-503 but like they say Hind Sight is 20/20. And where is a good place to get these amps Modded & Repaired ?

Thanks in advance
Mike
 
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I myself can only repair the little 203P amps. Managed to get a few back from the dead. I believe the KL-503 HD is just the KL-503 but without the 1 transistor to drive the rest of the amp. Just curious how many watts were you giving the amp? I honestly never go over 10 watts on SSB to the 203 and only do just under 2 watts AM swinging to no more than 8. Just to not upset the little amps.

Best case scenario, maybe its just that 1st transistor that drives the rest of the amp that went bad? Would be just as easy to bypass it. (There is a guide here with pictures as to what needs to be done to disable that part.) This way, you can use your radio to drive the amp instead. If you feel comfortable, may as well pull the cover off and get a picture of the board.
 
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doffo said:
I myself can only repair the little 203P amps. Managed to get a few back from the dead. I believe the KL-503 HD is just the KL-503 but without the 1 transistor to drive the rest of the amp. Just curious how many watts were you giving the amp? I honestly never go over 10 watts on SSB to the 203 and only do just under 2 watts AM swinging to no more than 8. Just to not upset the little amps.

Best case scenario, maybe its just that 1st transistor that drives the rest of the amp that went bad? Would be just as easy to bypass it. (There is a guide here with pictures as to what needs to be done to disable that part.) This way, you can use your radio to drive the amp instead. If you feel comfortable, may as well pull the cover off and get a picture of the board.
Click to expand...
I set the AM dead key at 1-1.5 but never set the AMC down but with all my fooling around maybe the dead key got turned up and didn't realize it. I wouldn't mess around inside these amps with no training. I'll try my KL-300P instead of the 503 and see what happen. I figure those RM Italy amps are cheap for a reason but I will open up the 503 to see if anything looks burnt. I'm reaching the end of the line for my radio investment but I will say I Re-hooked my Cobra 2000 back up and it seems to be working fine with it's extra channels. I sure wish I would of had some radio training early on ! And I have to get my Palomar 300A fix because that worked good until the pre-amp went South.
Thanks for the reponse !
 
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FlyBoy50 said:
I set the AM dead key at 1-1.5 but never set the AMC down but with all my fooling around maybe the dead key got turned up and didn't realize it. I wouldn't mess around inside these amps with no training. I'll try my KL-300P instead of the 503 and see what happen. I figure those RM Italy amps are cheap for a reason but I will open up the 503 to see if anything looks burnt. I'm reaching the end of the line for my radio investment but I will say I Re-hooked my Cobra 2000 back up and it seems to be working fine with it's extra channels. I sure wish I would of had some radio training early on ! And I have to get my Palomar 300A fix because that worked good until the pre-amp went South.
Thanks for the reponse !
Click to expand...
I have a 350z from my old man. It has not been powered on since the early 1990s... I know better than to just plug it in and go. At this rate, the capacitors and such need replacing. But from what I understood, the 350z isnt an amp to run. I was hoping I could get mine gone through and be brought back to life, but Nomad mentioned that how the amp is and operates, it just isn't worth the effort.

It will sit pretty for awhile now. Maybe just run your Cobra 2000 on that 300A. The Quad 6 might be a bit too tough. :)
 
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Eldorado828 said:
That's entirely too much radio for that amplifier! That radio swings 90 to 100 pep. And even if you turn it down, it's asking for trouble.
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Now that is a good thought ! I hear and feel those Old Gears starting to turn again and smoke is coming out of my ears. You created a Monster ! LOL
 
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FlyBoy50 said:
I've thought of that approach but not in this stinking Valley
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With all due respect that seems completely backwards to my way of thinking. Your down in a "stinking" valley and can't get out on DX. Surely upgrading the antenna in some way is the obvious solution to the problem at hand? What approach were you hoping for to solve the problem? Just throwing more power at the problem isn't going to help.
You asked a question about a problem and the folks on here have given you a path to a solution which is upgrading the antenna.........
 
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BC Coyote said:
With all due respect that seems completely backwards to my way of thinking. Your down in a "stinking" valley and can't get out on DX. Surely upgrading the antenna in some way is the obvious solution to the problem at hand? What approach were you hoping for to solve the problem? Just throwing more power at the problem isn't going to help.
You asked a question about a problem and the folks on here have given you a path to a solution which is upgrading the antenna.........
Click to expand...
I was advised by more than one old time radio person that the way the Star Duster radiates the signal it is probably my best choice for getting out of this valley and it seems to work. The problem is I'm now fooling around with these new 10 meter more powerful radios so maybe I need to cut the Amps out of the picture as suggested. I've been involved with other radio forums with a lot of old time radio people. I think I will try Eldorado828 suggestion and cut the Amp with the new stuff and see if the radio sings on it's own and isn't drug down by Amp SWR problems. Lord knows my SWR is great without the Amp. It's a matter of This Old Dog needs to learn New Tricks ! LOL
 
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First thought was the KL503 in either version is pretty much a low drive amp. That's a pretty hot radio for that amp. If the RF power on the radio can say dial SSB peak power down to 12-20 watts then it would be usable. On AM maybe 1.5 watts swinging 10-12. Many new radio's still swing pretty hard even from a low dead key so AM use might not be possible.

All you can do is double check your install. Big enough power supply, good ground, good 3, 6, or 9 foot jumper or jumpers if you have a watt meter in line. If this is a base check that your antenna is in good order as well as coax.

If you have a different low powered radio to test with that amp give that a try. If all else fails then the amp probably has an impedance mismatch. It would have to be sent our for some work. If you google "KL503 amp problems" plenty of videos and an AI explanation will pop up. Good luck.
 
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