KL503 junk

[KD2GOE]

I got this amp so I can shoot DX when I go camping.. was running the RM KL503 with my cobra 148 all I did was use it on low power pushing about 10 watts max SSB in to it, and getting 110 watts out. and I was sound ruff to people... so I took it with my 148GTL to the shop get set up well it came back bad predriver he replaced it with a IRF520.. ok cool I used it a few times pushing 100 watts on setting 1 no complaints. and now every one tells me it sounds like trash... WTF...

Ok before I just through this in the trash.. can I replace the IRF520's with IRF540? will that help beef it up?

And I am looking ac the kl503 schematic and this looks to me like a class C not a Class AB :sad:

if I cant save this thing I am going to strip all the switches and fuse holders out of it and through it in the trash

 

[Robb]

Are you sure that the AM Limiter wasn't removed?
That is all it would take to sound nasty on SSB . . .

 

[Rebel Son]

I got this amp so I can shoot DX when I go camping.. was running the RM KL503 with my cobra 148 all I did was use it on low power pushing about 10 watts max SSB in to it, and getting 110 watts out. all I was getting was I sound ruff to people... so I took it with my 148GTL to the shop get set up well it came back bad predriver he replaced it with a IRF520.. ok cool I used it a few times pushing 100 watts on setting 1 no complaints. and now every one tells me it sounds like trash... WTF... ok before I just through this in the trash.. can I replace the IRF520's with IRF540? will that help beef it up?

And I am looking ac the kl503 schematic and this looks to me like a class C not a Class AB :sad:

if I cant save this thing I am going to strip all the switches and fuse holders out of it and through it in the trash

I helped a friend of mine who had a CB shop when I had Fridays off. I could not believe the junk they are putting out these days and what they are wanting in price for it. We would take brand new radios out of the box before a sale and put them on the sig gen to get them right. There is no quality control anymore on what is hitting the market. It was a wake up call for me when I worked there. I would check as Robb said about the AM limiter. That's the worst thing you can do to a radio is remove the limiter. But a lot of people do because they love to see swing on the watt meter not knowing on how badly it effects audio quality.

 

[ExitThirteen]

Don't throw it away. Send it to me as is, and I'll experiment on it. I'll see if I can implement some biasing to it. I'll even pay you a little bit for it, and pay for shipping, but DON'T THROW IT AWAY!

Shoot me a PM with some info, and I'll get back to you.


~Cheers~

 

[AL567]

Hate to hear that mkube. Guess I've been lucky so far with mine. hope you can get it fixed.

 

[KD2GOE]

Are you sure that the AM Limiter wasn't removed?
That is all it would take to sound nasty on SSB . . .

the radio was all put back to stock.. every thing is intact just unlocked the clarifier

I have ran it with 3 radios same outcome

Don't throw it away. Send it to me as is, and I'll experiment on it. I'll see if I can implement some biasing to it. I'll even pay you a little bit for it, and pay for shipping, but DON'T THROW IT AWAY!

Shoot me a PM with some info, and I'll get back to you.


~Cheers~

I am also looking at implementing some type of biasing to help it out.. I am looking at the schematic and seeing if I can re do it in LTspice

If I cant get it down on paper first and I give up ill let you know...

 

[basstracker1970]

I have run a KL-503 for years now with a galaxydx2527 and many other radios. I have gotton nothing but praise on the loud clear sounding audio. Something must be wrong with yours I love mine it works awesome.

 

[KD2GOE]

any info on the IRF540's?

 

[ExitThirteen]

IRF540's won't work. I've experimented with them, and all they do is produce heat, then burn up in RF applications.

Best way to go is with the IRF520N's from International Rectifier. That's all I use when replacing mosfets and/or modifying radios to use mosfets. The IRF520N's are a little more rugged than the regular IRF520's.



~Cheers~

 

[Klondike Mike]

I got this amp so I can shoot DX when I go camping.. was running the RM KL503 with my cobra 148 all I did was use it on low power pushing about 10 watts max SSB in to it, and getting 110 watts out. and I was sound ruff to people...

I can concur with your finding. Initially got good reports but I'm assuming people weren't listening close enough. Started to get negative reports from better ears and unit is now back in the box.

 

[KD2GOE]

IRF540's won't work. I've experimented with them, and all they do is produce heat, then burn up in RF applications.

Best way to go is with the IRF520N's from International Rectifier. That's all I use when replacing mosfets and/or modifying radios to use mosfets. The IRF520N's are a little more rugged than the regular IRF520's.



~Cheers~

ok bummer good to know...

I clipped each one out and tested them and then reinstalled them they all tested fine according to when I see on the internet using my diode tester

 

[KD2GOE]

Exit13

This is the kl503 schematic it looks like it has biasing I traced it in red does this look right to you?
it looks odd as it had to pass through the transformer to get to the other fets but I guess it doesn't matter as it is only DC...

 

[KD2GOE]

ok well I have it working good I have been looking at schematic all day comparing most of the RM line of amps.
now talking to my friends and they gave me good SSB auto reports. :drool:

what I did was just disable the pre-driver on the amp and bypass it. i have included a pic.. you can all so just cut the pre-driver out and cut R26 and C30 but I didn't feel like removing the board...

one nice thing is I don't have to drive it so low now. I would like to get it on a scope at my friends so see how the single looks but from what there telling me I may be fine.

on SSB with 15-18 watts PEP drive
Setting 1 30 watts pep
Setting 2 70 watts pep
Setting 3 100 watts pep
Setting 4 150 watts pep
Setting 5 200 watts pep
Setting 6 250 watts pep

on AM I have it set on 4 watts DK swinging to 18
Setting 1 DK 5 swinging 30
Setting 2 DK 20 swinging 70
Setting 3 DK 25 swinging 90
Setting 4 DK 30 swinging 150
Setting 5 DK 40 swinging 200
Setting 6 DK 50 swinging 225


that is with just giving a soft audio in to the mic dont want to wake the wife over all I am really happy with this amp now that it is working. ill see if it lasts with the job I did to it...

 

[ExitThirteen]

That looks about right. I don't know why they'd have 1 driving 8 tho... no wonder that driver went kaput on you... would interesting to swap in an ERF7530 in place of the IRF520 in the driver spot, re-bias it, and see how that would do, you could drive it with a single final CB and not have to worry about over driving it. However, it might be too much input into the final stage. Maybe I'll have to order one of these KL503's, or if I find someone that wants to get rid of one that's broke or cheap. Be fun to experiment.


~Cheers~

 

[KD2GOE]

when I was running it with the predriver I was hitting it with (1watt DK swinging 8) on AM and just swinging 8 watts on SSB

yeah I was thinking what would I see if I swooped in 8 ERF7530. but that may be to much for the transformers?? the 1 100ohm resister on R8 would have to be beefed up...

putting in 8 ERF7530 might make the amp do what it is ratted to put out LOL! 120 watt DK with 500 watt swing