RM Italy’s KL800 Amplifier

Finally got to have a look at the KL800 Amplifier.
All looks real good on paper…4 ea 422 transistors, large heatsink, 3 fans, 28 volts DC input.
I have been waiting for a while to check this one out.
Is the reign of the Texas star DX500 about to come to an end?
On paper yes! Slam Dunk! 50% more disapation from the transistors 150W PEP  for the MRF 422 vrs 100W PEP for the 2879.
We know we can push 4ea 2879’s to 600w PEP quite comfortably so we might be good for close to a KW with this!! RM did label it the KL800 for a good reason I am sure. The back panel indicates 13.8V input ..hmm..bit of lack of detail there…..it also doesn’t have a dedicated PTT on the rear….they are not too serious about this as an amp then. LEDs look nice though.
Lets check out the labeling. Not quite sure what the yellow one is trying to say but the rear one has the voltage at 13.5V and the manual says 28V.
Ugly way of securing the bottom panel. The boards are nice inside but the the bottom panel is secured is pretty bad. Material very light and flimsy to boot.
Same as the HLA series of amps.
The front panel…See the green bar on the left of the face. It is just a design mark. I don’t know what ourput power they are talking about. No way to work out what this amp is doing without a power meter after it and amp meters on the DC in.See what I mean about the LEDS.
Nice bright front panel with toggle switches. I like toggle switches. They don’t get knocked about in transit like knobs and wafer switches. And the fans. Three of them. running gently all the time and speed up when you key the amp. They don’t make much noise..but then they don’t move much air either! Have a think about it..what on earth can the middle fan do? Where can the air go? At best it cuts down on the eficiency of the other two and at worst it uses up valuable fins that could be disapating some heat. One big fan in the middle would work a lot better and cover more of the amp. But the 3 fans looks cool and hey..we are Italian.
The first switch is the AM/SSB switch. I turned it on thinking it was the on/off and nothing happened. Oopps. The next one is the receive amplifier. That works really well. Signal and audio came up well without a lot of additional noise and no broadcast stations. And a cute yellow led telling you it is on. If I have a choice I won’t buy an amp with a receive amp built in because they only serve to increase the noise and lose inteligibility. This one didn’t. It actually worked well and I left it in because it helped!!! And The yellow LED looked cool.

Number 3 is the on /off. (Cunningly concealed in the middle to make it more difficult to find. )

Last of the toggles is the power input switch. You have a choice of 5/10/15 watts input. The LED colour changes depending on the setting. I guess we will have to read the manual to find what mode the powers refer to.

How can you drive 4 422’s in parallel with only 15w? Most radios sold today are at least 30W.  Hope it is AM. Better check the manual.
What segment of the market is this designed for?
The manual says the following:
Frequency 24-30mhz
Supply 22-30 VDC
Input Energy 10-30Amps (quick calc here; 30 amps x 30 volts x 65% = 585W)
Input Power 1-15W AM/FM
                   2-30W SSB/CW
Output Power 200-600 AM/FM
                     100-1000W SSB/CW
Input SWR   1.1-15  (I didn’t check, later when we look at the band width)
Mode           AM FM SSB CW ( I have ny doubts about CW!)
Fuse            3x12A
Nicely laid out inside and quite neat. The RF input side looks pretty tiny, the cobiners and splitters don’t look like they could handle much and the output combiner does not use any toroids which probably restricts the range of the amplifier. Strange colour and material of the ferrites used in the output transformer. Looked like cement. Maybe Rm are rolling their own now.?
Ok fire it up…Did a couple of quick tests into the dummy load and all seemed good. More on the power later as I didn’t get time to take any notes.
It was working so lets get on air. I used a Magnum 257 with about 30w out and set the input switch to 15W on the kl800 and called test on 555 to have a look at the SWR on the antenna. It wasn’t good. 1.7 but we will try it for now. To my surprise geoff in Darwin came right back and asked me what I was doing. Where did you come from? The band is quiet ! It has been dark for a couple of hours. Not any more mate! Out put power 250 W PEP. Tried on the middle setting and saw 600w on the meter before the protection took the amp off line. No indications anything amiss, just wouldn’t key. Ooooppps. Thought I had blown it for a minute. Turned it off and on and she was right back. Over drive or over SWR not sure but will check it later with the dummy load to see. Some indication that the protection had kicked in would have been useful here. Protection is good..I like it. In the old days only the really expensive Solid State amps had protection built in but now we are seeing it more often…our new broadband 2-30mhz 500w amps have it built in also. Coming soon! Shipping next week.
So we talked on for a bit about this and that..had been a while since we had caught up..and the output was dropping a bit…I have noticed the MOSFET finals in the new radios do drop off when they warm up so wasn’t too concerned….until I put my hand on the heat sink of the amp. I could hardly hold my hand on it. For running 250w out something had to be wrong. It shouldn’t get this hot. I know folks say you can run solid state devices till the solder starts to melt but I don’t feel comfortable with that. I work better when I am cool and I expect my amps to to the same. Time to switch it off. Unplugged it and stuck it front of a large room fan to help it cool off. I opened it up probably 5-10 minutes later and the heatsink had cooled off completely but the ferrite material in the large toroids was still very warm to touch. Hmmmmm. I think RM have missed the mark with this one. While we know the transistors can do the job it is doubtful that the rest of this amp is up to it.
It is 28V so can’t be used mobile without some additional equipment, no indication on the amp as to what it is doing, and the heat…..
While it may keep up with a DX500 in the 500w power stakes it won’t do it for long. After RM have had so much success with the KL500 this amp should have been a 750W power house. Twice the power, twice the heatsink, twice the volts in…..but somehow the sum of the bits does not add up to what it should be capable of. I think RM will need to go to version 2 in a hurry.
More tests on the dummy load when I get some time.
Sometimes we don’t expect much but are pleasantly surprised, the magnum TX 2000amp was like that. Sometimes we expect a lot and the goods don’t live up to it. I don’t think this is good value for money. The heat build up with 250w out does not bode well for this amp at higher outputs. You may as well buy a KL500 at less than half the price. In fact 2 Kl500 boards in that case and heatsink would probably make a much better amp! More tests to come.
The DX500 is still the King!!
There are some power LEDs behind the green front panel indicator. Just can’t say I saw them. Will try it with the lights off and see if they show up!

About David Donaldson

64 and Live in Jakarta, Indonesia. like to ride my bikes.
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9 Responses to RM Italy’s KL800 Amplifier

  1. Dave says:

    Made a booboo. Was putting the amp back together and noticed there were some LEDS behind the front panel. I just don\’t recal them coming on. I did have a bright desk light on. Will test later when I get the 28v back in line.

  2. michael says:

    very nice reveiw there really a great help. i have this amp myself picked it up for 130qid can you suggest a good power supply for it for homebase use? i saw one on ebay its some chinna rubbish but i dont know if its any good it a 1000watt psu 24v at 40a its ment to be designed for radio amps and so forth but i dont know if i can trust it being at such a low price of 120qid. can you reccomend?

    • dd182003 says:

      I would go for the chinese supply! It will do the job well. I use quite a few of the small 30A 13.8v switch mode supplies here myself!
      Watch the KL800 under use..it will heat up and back off power if you drive it hard. Only needs a touch of drive…
      Give me an amp that won’t balk at 50w input any day!
      For the money try it, make sure it works then sell it off and get a DX500 13.8v amp that you can run in the car as well!
      Remember…watch the drive and keep it low…….

  3. michael says:

    im going to be using it homebase and its a 24v dc amp not a 13.8v

    • dd182003 says:

      Understood but I am recommending you sell the KL800 and get something that runs on 13.8v for greater versatility.
      let me know how you get on with the kl800 and what radio will you be using with it?

  4. michael says:

    hi there again just rememberd about this thread, yeah i still have amp sadly its seen better days i must admit sadly the command board inside will need replacing as the prevoius owner cut the ribbon cable and extened it. saldy he or she has done such a bad job of rewiring i now have to find a new command board. the main board is intact and the finals are not blown but i cant use the amp until i get a new command board anyone know were i get get parts? ive contact rm kl directly so fingers crossed. 🙂

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