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Rm Italy KL-503 watts vs amps

1 irf520 driving 8??? Seriously? Seems pretty stupid. May as well just be a straight 8. It would be much more versatile. Though, I suppose it would be hard to blow the final stage in that unit. I suspect the driver gets pretty stinking hot though.


Yes it is dumb I converted mine to 8 mosfets and bypassed the driver I get 200 clean watts out. I can drive it to 250watts pep if I push it.
I am now driving it with 20watts pep to get full power bypassing the driver helps alot.
I run my KL-503 on SSB @ 10 watts PEP (max via a 1 khz tone so usually under), the variable switch is at 4, and I peak at 200 watts. I have no complaints and the reports I get are all positive.

On the odd chance I am on AM, 2.75 watts dead key swinging to 10/11 (again, via a 1 khz tone so usually under) and I get the same 200 watts peak.

I do get more out of it if I switch the variable output but have non need as it seems happy where it is.

Power supply is a 40 amp unit powering the KL-503. The radio is on it's own power supply.

ETA - these numbers are for a Uniden Grant XL
I get similar numbers from an Optima (10 watts SSB PEP) but I drive it less on AM and the Grant has more audio in both modes.
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Well, everything ive heard has been pretty positive in terms of audio. It seams like the power is just over rated.

The 2979N2 and galaxy 98 both run 8 mosfets driven by 2, driven by 1 and they won't come close to the advertised 450w of the 503.

At any rate, for $189 thru copper it seams reasonable.

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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.

Whoopsie daisey you are correct. The transistor that is listed on the parts listing is the Mysterious "RM3". Irf520 and any other FET of specifications will work if you adjust the bias.

The ERF7030's are in the Black Cat linears.
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The things I learn from you people on WWDX is incredible. That is absolutely the best description of how to figure out the output af an amp. Thanks CaptainTE="Captain Kilowatt, post: 486519, member: 39"]Typical RM rating IOW bullshit rating. They typically rate something at nearly twice what it will put out. The big clue is the fuse rating. Mulitply the fuse rating by 13.8 volts and then divide that result by two and you will be close to the actual power output. That amp draws 30 amps so 30 x 13.8= 414 watts 414/2 = 207 watts which is more inline with reality. A typical 100 watt ham transceiver requires about 20 amps of current. Some need 25 amps. Getting 450 watts with just 30 amps draw absolutely defies the laws of physics since it would require the amp to be MORE than 100% efficient. RM is one of the worst for overstating ratings however most CB amp manufacturers do the same thing.[/QUOTE]
Year old thread but I ended up getting a few kl-503's. I bypassed the driver. It wasn't getting enough juice to the 8 finals (duh-what the heck). My 2950 drives it very well and despite the power readings being below 250 PEP, the carrier is quite high with 2w input, which I actipually like. Very efficient ever since I got rid of the driver. Honestly, I love this amp. VERY IMPRESSIVE for $150 shipped.

Going to test the 505v now. Hope the 455's hold up.

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