Rm Italy KL-503 watts vs amps

[Super60]

Well my Kl-503 is out for delivery today. My modest setup will include my factory stock President McKinley, a Megawatt 400 power supply and a MFJ power meter all going to a dipole antenna outside. I have been running a kl-203 and the McKinley as a mobile and a base. With 10 watts in on SSB to the 203 I am getting 100 watts PEP as a base. Looking forward to see how the KL-503 does.

 

[Dereka5]

You guys thinking about the KL503, please seriously consider the KL505 instead.

RM isn't particularly good as we all know, but the KL505 is a much better bit of kit than that 503.

 

[Super60]

You guys thinking about the KL503, please seriously consider the KL505 instead.

RM isn't particularly good as we all know, but the KL505 is a much better bit of kit than that 503.

I'm sure you are correct that the 505 is better than the 503. I bought my 503 for 195.00 US Dollars and the 505 is 338.00 US Dollars so I hope it is better. These prices were at 88radio.
I did get my new KL-503 up and running with my President Mckinley and so far I am very happy with it. Learning from this forum especially was the wisdom to err on under driving it and not try to squeeze every last watt out of it. My SSB swings to about 10 watts and when on AM I turn it down to a 1 1/2 dead key but rarely use AM. My power level on the 503 is set at 4. Everything seems very happy and have had good reports on SSB. On my MFJ-870 meter I am seeing 200 watts with some minor swing a little higher than that. Amp is cool ,power supply [Megawatt 400] has no problems running both the Mckinley and the kl-503. I have talked all over the midwest to TX all the way to FLA and in between on my Mckinley on a small kl-203 and a Dipole so I realize no amount of power will help if Mother Nature is not in the mood. I know these distances are nothing to you experienced guys but it is a real thrill for me as I am just getting into this. Anyways thanks for listening and so far so good.

 

[g3vbv]

I am getting low power out from my KL505. It was OK a few days ago.
SSB power input is 5W.
Output was 250W PEP, now it's only 20W PEP.

 

[ForestRunner98]

I am getting low power out from my KL505. It was OK a few days ago.
SSB power input is 5W.
Output was 250W PEP, now it's only 20W PEP.

What radio are you using? 5w is the swing or where the radios power is set to?

 

[nomadradio]

It was OK a few days ago.

Raises the question, is the radio still delivering the same drive power as before?

If so, the amplifier has broken.

73

 

[Mikey1966]

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.

I put a 15 pf in mine, removed the 3.3. It seems ok now.

 

[Mikey1966]

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.

I put a 15 pf in mine, removed the 3.3. It seems ok now.

Frequency 3-30 Mhz, HF amplifier, with 2 cooling fans,
Mode AM-FM-SSB-CW (This amp does not work well with Flex or KX3)
Input power: 1-15 W AM/FM, Input power: 2-30 W SSB/CW , Output power - 300 W Max AM/FM, •Output power: 600 W Max SSB/CW
Supply 12-14 Vcc, Output power level - 6, Antenna preamplifier - 26 dB
Made in Italy, This model is for export only, only ship to the address outside of US

The KL503HD will never see 600 pep. I removed the -7db attenuator & it produces more power. Ssb radio peaking 8 watts pep the amp makes 320 watts. Anymore power it doesn’t produce anymore so I leave it at 8 pep out of my ic718.

 

[Brother DXer]

I put a 15 pf in mine, removed the 3.3. It seems ok now.

The KL503HD will never see 600 pep. I removed the -7db attenuator & it produces more power. Ssb radio peaking 8 watts pep the amp makes 320 watts. Anymore power it doesn’t produce anymore so I leave it at 8 pep out of my ic718.

You're right, this amp wasn't built or advertised to run more than 300 watts. Yes, you can squeeze a few more out of it, but 600?? That's just idiotic. Gezz, the lack of intelligence has me concerned about planet earth.

 

[Mikey1966]

The 503 uses erf7030 fet's and the other uses the no longer in production MS1051. Rm Italy has re-biased the unit that uses MS1051 transistor to run the MRF 454.
The re-bias is necessary, RM Italy says it is not a direct drop in replacement. If the bias is left as is they warn of possible further damage to the circuits.
The kl-505 is more of a ham amplifier because of the frequency range 3MHz to 30 MHz.

The kl503 doesn’t even use the mrf454 case style type transistors. They use case style transistors the same as the finals in the Anytone AT6666 radio uses.