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Surgeon needed for RM Italy KL503HD

I'm off to a flying start today attempting to install the new mosfets.

Here is a link to the mosfets I bought. They are stamped with "IRF520 N26K AD".

I figured I should test them out before installing them so I following the same steps with them as I did when testing the original ones I removed.

I set the multimeter to diode test. With the mosfet's metal backing away from me, I have gate is the leftmost pin, drain is the center pin and source is the rightmost pin. I touched black to source and red to drain to meter remained at 0. Then I kept black on source and touched red to gate for a second then moved red back to touch drain. There was still 0 reading on the meter. When I did the same steps on the original mosfets, this last step produced a meter reading of .049 to 0.70 except for the original driver mosfet which remained at 0. I replaced the multimeter's batteries and repeated the test on the new mosfets but they all still read 0.

Did I order the wrong IRF520s or am I testing them incorrectly or?

Replacement.jpg
 
I just saw a site with a different way of testing the mosfets. With the red lead on source and the black lead on drain, I do get a positive reading of about 0.54 on the new ones so that tells me they are good. But then I tested the original driver mosfet and it passes this test too. I also did the resistance test and they return a positive value. I may just roll the dice and have at it. I'm tired of jacking around with this and pestering everyone on here about it.
 
It's all back together now. Result is it is way down on power and the audio on SSB still sounds like @#$@#. I am using a bone-stock President Mckinley SSB radio to test it out.

I'm done screwing around with it. If I can find a shop to send it in to for professional repairs, great. Otherwise it's going on the shelf in case it gets some governor's reprieve in the future. Or maybe eBay. Who knows.

Now to find a good amp in the 300 to 500 watt range that will not break the bank, that will work with my President Lincoln II+ and maybe even a toned-down Anytone AT-5555N II... but I will probably just stick with the Lincoln. The replacement amp absolutely must sound clean on SSB. I hate ones that don't.
 
It's all back together now. Result is it is way down on power and the audio on SSB still sounds like @#$@#. I am using a bone-stock President Mckinley SSB radio to test it out.

I'm done screwing around with it. If I can find a shop to send it in to for professional repairs, great. Otherwise it's going on the shelf in case it gets some governor's reprieve in the future. Or maybe eBay. Who knows.

Now to find a good amp in the 300 to 500 watt range that will not break the bank, that will work with my President Lincoln II+ and maybe even a toned-down Anytone AT-5555N II... but I will probably just stick with the Lincoln. The replacement amp absolutely must sound clean on SSB. I hate ones that don't.
Buy a davemade
 
Well I took the plunge and ordered a Carl Built amp. Fingers crossed it works well.

Now to figure out what to do about the KL503HD I have been tinkering with for the past few weeks. The extent of the tinkering was to replace the 9 mosfets.

Are there any brave souls on this board that want to earn some extra money to have a look at the amp and determine what it would need to make it work well at least on AM? Bonus bucks if you can do the same for SSB. I'll pay shipping both ways plus bench time. You may look at it and determine it is foo-barred and just send it back to me. Or you may see that it's a simple fix and maybe even the driver bypass is attainable. Or even a colleague/friend/acquaintance that knows their stuff and may take this on? Anyone?
 
Well I took the plunge and ordered a Carl Built amp. Fingers crossed it works well.

Now to figure out what to do about the KL503HD I have been tinkering with for the past few weeks. The extent of the tinkering was to replace the 9 mosfets.

Are there any brave souls on this board that want to earn some extra money to have a look at the amp and determine what it would need to make it work well at least on AM? Bonus bucks if you can do the same for SSB. I'll pay shipping both ways plus bench time. You may look at it and determine it is foo-barred and just send it back to me. Or you may see that it's a simple fix and maybe even the driver bypass is attainable. Or even a colleague/friend/acquaintance that knows their stuff and may take this on? Anyone?
Well there might be someone out there but if there isn't post it for parts on here. I might be interested if the carcass is in good shape, I've got 2 of them and never know if something fails. Would be good to have parts on hand.
 
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Well there might be someone out there but if there isn't post it for parts on here. I might be interested if the carcass is in good shape, I've got 2 of them and never know if something fails. Would be good to have parts on hand.
That "carcass" reference was a good one. Got a nice chuckle out of the imagery. I can transfer a new piece of electronic equipment into a carcass in record time.
 
  • Haha
Reactions: Eldorado828
Hi.
Original RM3 fet is IRLZ24 or IRLZ14 can be used.
IRF510 will work better then 520 but bias is different vs. IRLZ24
RM4 is still unknown?.

Driver with 1 fet is bad idea and makes horrible rf.
I have removed it my own KL503.
Also original biasing is crap.
8pcs IRLZ24 @27v 12w drive 250w out FM 27MHz
 
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