I have a 503 with my McKinley and I get get reports on AM and SSB. Don’t overdrive them and you will be golden.
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RM Italy KL 503 HD - Anybody ever use?
- Thread starter Wire Weasel
- Start date
I've got 2 of the HD versions purchased from a forum member and he had nothing but good to say about them. I have yet to use one but plan on running one with a Texas ranger 797. I hope to get the result @NightThumper had with it.
I have 4 of them, work great drive up to 35 watts P to P and you will love this amp
must not be set up correct mine sound fine in AM or SSB and put out around 250 watts P -P no more than 35 watts P -P input
Local guy has a 503, works fine on AM sounds like garbage on SSB. He has tried 3 different radio's with as little a 5-6 watts and as much as 25-30 PEP input on SSB. There have been others here on the forum that have had the same issue. I just don't think it's the best choice for SSB use. Looks like this class C box is a love it or hate it type amplifier.
I had one put on scope and spectrum analyzer at DTB. the 503 HD is a 200 watt amp. My settings are AM # 5 and SSB #4 Max settings or it distorts. Output around 225 watts AM, just under 200 watts SSB. Its fine is you do not expect any more. I am fine with 200 watts. Using TR 696 FD-1 with 5.5 watts swing to 28 watts. Hope this helps out.
secret squirrel - Have you experimented with a low pass filter. I use one just because of the fact I run an amp. I also keep my mic gain turned down a little and never shout. I just speak normal and clear. The 503 HD I run gets very nice reports, running it on 6 with around 30 watts swing going in. It's putting out around 325 watts. I'm extremely mindful about sounding shitty and would rather run barefoot if need be. Actually, I only run the amp whenever I'm not getting out with a barefoot Stryker 955 or AT-Q5N2.
BUT... This is MY experience and it's all I can speak on.
No amps sound bad on sideband. Amps simply amplify what you put into them. Put good in - get good out. Put trash in - get trash out.
Greg T
WDX-945 (Jazz Singer) Upper Peninsula of Michigan
I find myself having to disagree with this. My buddy, after a boatload of troubles with his entire system, finally has been up and running for over a year now. I won't go into the long and dragged out details, but to shrink the story I'll explain what he did to get going. He now has a striker 955 that I personally set up and sounds absolutely tremendous on all modes while barefoot. When he kicks on the 503 his modulation is Harsh, choppy and clipped. While setting this up I've tried various dead keys as well as Peak power settings to get it as best we could. Currently the best sounding set up on his is a 2-watt dead key swinging to 14 watts pep. And the amp still sounds like garbage. On SSB we set it up for 16 Watts pep to get the best sound we possibly could. Just setting the radio at the amplifier settings, the radio itself sounds absolutely tremendous. Simply kick on the amplifier without touching anything else in the audio turns to garbage. I have only played with two RM Italy's in my entire life, the 203 that I had years ago sounded okay went out over driven. But this 503 has absolutely no setting where it sounds good.
It's been my experience if the amp is not biased properly and you run it on SSB, there will be distortion. Some worse than others but it's there.
I have switched back and forth from a Biased amp and a class C amp with delay on SSB and my brother can instantly tell what amp I am on, even if I try to trick him.
I have had him on my base doing the same, listening in the mobile and it's there.
Running the same 2510 driving both.
I added a delay to a TS Mod V years ago and tried using it on SSB, it was horrible on air.
Not as bad on AM mode, and really, most of the AM junkies on 11 meters don't worry about it anyway, but it will show up on SSB.
73
Jeff
I have switched back and forth from a Biased amp and a class C amp with delay on SSB and my brother can instantly tell what amp I am on, even if I try to trick him.
I have had him on my base doing the same, listening in the mobile and it's there.
Running the same 2510 driving both.
I added a delay to a TS Mod V years ago and tried using it on SSB, it was horrible on air.
Not as bad on AM mode, and really, most of the AM junkies on 11 meters don't worry about it anyway, but it will show up on SSB.
73
Jeff
I just had a nice qso with 200 (two double 0) Ray in Australia. He was sounding choice and gave me (in his words) an excellent report as well. Using the 503 HD. 
"IRF520/ERF2030's are the replacements for the KL503 NOT ERF7030's !
My KL503 only produces 150 linear watts anything more saturation is noticeable.
For SSB operation i also had to increase C34 by 12pf to provide enough bias to TR2. If you have choppy audio with your KL503 then this mod should fix that."
From Joe dirt
My KL503 only produces 150 linear watts anything more saturation is noticeable.
For SSB operation i also had to increase C34 by 12pf to provide enough bias to TR2. If you have choppy audio with your KL503 then this mod should fix that."
From Joe dirt
Well said. Many years ago I had a Joker 2 pill that had Peakaboo's regulated AB bias. When a group was talking I would switch to a different amp from time to time. There were two guys that would call me out right away.