RM KL-203 and Repair

[Robb]

I put irf520's in a friend of mine's little 203 that he over drove and burnt them up. they worked fine in the amp. a lot cheaper than the rm3 that comes in them. a little less output but not enough to justify buying the original ones. his put out about 80 watts after the mosfet changes on am and about 150 on SSB

Thanks for that tip. Was the bias voltage set at 4v/ea; or were all of the gates wired using a 4v regulator, or using a voltage divider? One more thing, how much drive/input watts can they handle per device?

 

[JoeDirt]

Thanks for that tip. Was the bias voltage set at 4v/ea; or were all of the gates wired using a 4v regulator, or using a voltage divider? One more thing, how much drive/input watts can they handle per device?

Pretty sure the KL-203 uses zener diodes.

FWI if anyone swaps mosfets in these little amp there are sockets that can be bought making the next swap a lot easier!

 

[Robb]

Pretty sure the KL-203 uses zener diodes.

FWI if anyone swaps mosfets in these little amp there are sockets that can be bought making the next swap a lot easier!

Thanks.
Never seen one of these MOSFET/RM Italy amps opened up and in front of me before, but I found a schematic for it and checked it out:

 

[KG0MN]

I am going to given you my 1,000,000 dollar secret for things like this. Go check out this link and watch the video.

SMD Removal using a Chip Quik kit - YouTube

The product he is using is call Chip Quik and it can be found at Mouser or Digi-key. Using this product you could of heat every lead of the relay at one time and pulled it of the board. I will keep solder liquid for about 40 second depending on the amount of solder on the component.

 

[Squints]

Can anybody advise me of whats wrong with my brand new kl203 rite out of the box it keys down and has output but when i let up on the mic the amp does mot unkey still transmitting until i switch off the power on the amp then the relay lets go and my receive is back on.
This amp does this everytime i key down and my watt meter goes all the way over when i unkey the mic snd amp still in transmit mode.
I cant return it so i gotta fix it so has any owners of this same amp ever had the same problem and fixed it ide like to know

 

[Squints]

Btw my swr is at 1.0 and im only pushing it with a 2 watt carrier and 6 ft jumper

 

[nomadradio]

Sounds like a less-than-perfect ground connection in one or the other of the plugs on the coax jumper.

A spare coax jumper might settle the question if you have one. If you have a dummy load, connect the radio to it with this jumper. Turn off the ANL and noise blanker. Turn up the volume until you can hear the radio's internal noise level. Now flex the coax where it comes out of each connector. A gentle twist motion will reveal if the braid is not soldered securely to the plug.

Any up-and-down jumps in the receiver's noise level will indicate the ground connection in that plug is iffy.

Maybe iffy enough to make the amplifier oscillate and hold itself keyed up after the radio unkeys.

73