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RM Italy KL 503 Crunchy

Discussion in 'Amplifiers' started by Greg T, Oct 4, 2021.

  1. Greg T

    Greg T 945 (Jazz Singer) Upper Peninsula of Michigan

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    Anyone have this issue with the KL503? My buddy just received his and I went to set it up for him. Instructions say 1 to 12 watts pep drive so I set up for 10 watts MAX peak and set the power knob on the amp on #4 so he didn't over power it for it's first run. Amp is peaking around 300+ pep. I went home to talk to him and the audio sux maggots. Esses are chopped, audio is crunchy, doesn't sound good at all. Wondering if we got a bad one or if it may be something else. He's running a 2980 with a D104. Without the amp the radio is clean clean clean.


     

  2. groundwire

    groundwire Sr. Member

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    Reduce input drive even more and see what happens
     
    binrat, L2, Greg T and 2 others like this.
  3. sp5it

    sp5it Master of puppets

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    Jumpers are properly bridged? Is bias working? What is the voltage on TR1 collector?
     
    Greg T likes this.
  4. Greg T

    Greg T 945 (Jazz Singer) Upper Peninsula of Michigan

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    You're speaking Greek to me. If you're asking if it's hooked up properly, yes. And the antenna match is 1.1:1.

    That's going to be my next step. Going to seriously limit it's output, but I guess lower/clean is much better than full/crunchy. That power knob on the amp... what exactly does that do? I mean, I know it lowers the output, but how does it do it?
     
  5. freecell

    freecell Well-Known Member

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    the "power knob" introduces different values of resistance between the amplifier input and the transistors to selectively pad or reduce the input from the radio or exciter. a lower power setting usually eliminates the crunch.
     
    NZ8N and Greg T like this.
  6. freecell

    freecell Well-Known Member

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    RM Italy KL 503 Mobile Linear Amplifier

    Frequency - 20-30 MHz
    Input current - 12-14 A
    Input power - 1 - 6 W
    Input power SSB - 2-12 W
    Output power - 250 W Max
    Output power SSB - 450 W pep Max
    Mode - AM-FM-SSB-CW
     
    #6 freecell, Oct 4, 2021
    Last edited: Oct 4, 2021
  7. Greg T

    Greg T 945 (Jazz Singer) Upper Peninsula of Michigan

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    Well, that's pretty much the way I had it figured. So, when I set it up for him I set his radio at 10w pep and used a #4 setting on the power knob. This peaked him at just over 300W pep (SSB) from the amp. I thought it would be perfectly safe there. Maybe I should back the radio down and try using #5 or #6 output setting. Couldn't padding the input cause distortion through those resistors?
     
  8. freecell

    freecell Well-Known Member

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    not likely.
     
    Greg T likes this.
  9. sp5it

    sp5it Master of puppets

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    I had a few amps with "power reducer" knob. Any other position than maximum breaks matching between radio and amp and cause problems.
    Another thing: test on dummy load, who knows amount of RF floating around.

    This 503 have driver transistor built in, so reduce drive from radio even to 0.5W AM carrier and check.
     
  10. Greg T

    Greg T 945 (Jazz Singer) Upper Peninsula of Michigan

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    He can't use it on AM because the radio is much too hot. The RF power control only goes from 16W down to 10W carrier. The low power pot inside has no effect. So this will be a SSB unit only.
    Although I didn't hear it at the time, I tested the amp on my Yaesu FT-990 @ 10W pep before we set it up at his place, and he said it sounded great to him. Now that it's at his place .... not so much. I will tell him to start at zero with a long count and slowly turn it up while I listen. And crank the amp wide open.

    PS. Just had a thought. His radio does about 25W pep on SSB. Would it be a simple task for a decent tech to bypass the driver and let his radio do a little more work?
     
    #10 Greg T, Oct 4, 2021
    Last edited: Oct 4, 2021
  11. 9C1Driver

    9C1Driver Sr. Member

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    Most of those RM amplifiers are low low drive and I'm pretty sure class C. Only thing I can think of is make sure all jumpers are good just to check. Then try backing the audio on the desk mic down a bit and back the mic gain down on the radio. In the end it just might not play well with that radio.
     
    Greg T likes this.
  12. Greg T

    Greg T 945 (Jazz Singer) Upper Peninsula of Michigan

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    Yeah, gonna try backing it off. As I said, he told me it sounded great with my Yaesu driving it. Now that I hear it on his Ranger it's bad. Real bad.
     
  13. Alexis Mercado

    Alexis Mercado Well-Known Member

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    I have this amp with a President Bill FCC. 3 watts carrier, 6 watts swing. I’ve been told it sounds bad when amplifier is at maximum power.

    I don’t understand why because the most I can get from this amp with this radio is 140 watts.

    How come is that ? I can understand if you overdrive this amp it would sound bad, but with only 6 watts maximum swing, I still don’t understand.
     
  14. Greg T

    Greg T 945 (Jazz Singer) Upper Peninsula of Michigan

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    Well, my buddy can only use SSB because his radio is too hot, and he drives 10 pep into it and sounds like SH*T
     
    Alexis Mercado likes this.
  15. groundwire

    groundwire Sr. Member

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    You get what you pay for. Rm italy, c'mon now, really.
     
    dave457 likes this.

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