RM Italy KL 503 Crunchy

[Greg T]

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.

 

[groundwire]

Reduce input drive even more and see what happens

 

[sp5it]

Jumpers are properly bridged? Is bias working? What is the voltage on TR1 collector?

 

[Greg T]

Jumpers are properly bridged? Is bias working? What is the voltage on TR1 collector?

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.

Reduce input drive even more and see what happens

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?

 

[freecell]

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.

 

[freecell]

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

 

[Greg T]

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.

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?

 

[freecell]

not likely.

 

[sp5it]

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.

 

[Greg T]

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.

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?

 

[9C1Driver]

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]

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.

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.

 

[Alexis Mercado]

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.

 

[Greg T]

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.

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

 

[groundwire]

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