RM’s KL703 500w PEP Amplifier Test

There hasn’t been a lot of new stuff to talk about recently with 10/11m in decline with the low sunspot cycle. Despite all that RM decided to send us a KL703 to look at which was very nice of them. 13.8v, 25 to 30mhz, 500w PEP and fans to boot! Where was this thing about 3 years ago when we needed it?img_20190122_151040

If you are looking for a 10 or 11m amp to run on 13.8v DC then look no further. This will do the job admirably.  We probably sold more of the little 100w KL203 amps than anything other than Optima radios over the years and now we have the equivalent of 4  kl203’s combined in a box without any driver stages (ala kl503) to mess things up. The KL203 was small, simple, sounded good on SSB, and was pretty tough for what it was..could be driven with anything from 5 to 15w with outputs approaching 150w on a generous meter and best of all it was cheap! Perfect companion for a 12w SSB CB radio.

Enter the KL703 !! Fan fare and drum roll……It ain’t small and I am sure with the fans, massive heatsink and quality board it won’t be cheap either. I doubt if I will be buying these for 4 times the price of a KL203. The heatsink of the KL703 alone is probably 6 to 8 times the effective area of the heatsink that came with the KL203. The input will also be around 4 times as much and same for the out put.


Told you it was big


This amplifier will mate perfectly to any of the twin final 10m export radios with around 25 to 30w PEP of output and produce a nice 400w PEP for you. It doesn’t particularly like the 12m band but for 10m and 11m it is pretty well fit and forget. No need to thrash it up to 500w as it will start flat topping. No output filtering. It is a CB amp first and foremost. The fans work all the time so should stop it heating up too much which is the bane of most mosfet CB amps. If you stick to SSB this thing should hardly get warm but certainly has the surface area to stay cool in AM and FM but further on air tests (10m only of course!) will be coming. img_20190122_191033img_20190122_190900img_20190122_190723

So who is going to buy it? Hams won’t touch it because it works on CB and has no output filtering and because it is made by RM Italy. CBers mainly buy cheap. This is not cheap. I don’t know what the USA prices are but I noticed it for sale in Europe for 498 euros. Not many shops were advertising it and I have yet to be advised the dealer price but as mentioned previously I can’t see it selling for 4 times the price of a KL203 because it is a lot more than 4 KL203’s. A lot more. A whole lot more. I would almost go so far as to say that this is possibly the best CB amp on the market today. It is one of the few true 400w mobile SSB CB amplifiers on the market. And here in lies the problem as I see it. It is a big fish in a small and steadily diminishing CB pond. It is a solid well made amp but can it sell in today’s market? Can it compete in the US of A with the US$350 price of the 500w Texas star amplifiers?

And that’s not all! Who is going to sell it? The FCC is spreading its cancerous fingers all around the world and it is getting harder and harder to import radio goods that do not carry some sort of approval. Sorry to say this amplifier will never get any approval from anywhere. It ticks all the wrong boxes! Which is a crying shame. Its a lovely amp and probably worth every penny. But I fear the horse has bolted. The KL703 just might turn out to be “too much, too late”
For me the sweet spot is still the KL505V.
How about sticking four of them in a box RM?
The Ham market is still buoyant and is crying out for a simple 13.8v, 1kw, mobile amplifier. Forget the filters. Lack of filters did not stop them buying the KL505’s. Hams like cheap too!

Want to see more? You can watch Mike’s video here.

I will go for a drive of it when I get back to New Zealand and pry it out of Mikes hands.

What doesn’t it have?
No output filtering. Could have easily been added as it is single band only.
No protection circuitry. Probably not needed. You would need to hit this with 60 or 70 watts input to hurt it and then it is only 50 dollars to replace all the transistors and it shouldn’t overheat with the oversize heatsink and fans. Hard to say what SWR it will take to cook it. Should always run a meter after the amp anyway and keep your eye on it. I hate it when Hi SWR circuit protection cuts in due to stray RF so simple is good in my book.

What does it have?
Clean SSB audio at 400w PEP
13.8v. You can run it in your car! Everybody is going to 50 volt devices these days so there is still a place for 13.8 stuff in the car. (That is until electric cars are mainstream and we have 50v DC to tap into)
Quality circuitry. It is well made.
Lots of cooling
Useless RF pre amp. Leave it off.

Anybody else got one of these?

Comments please!

About David Donaldson

64 and Live in Jakarta, Indonesia. like to ride my bikes.
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6 Responses to RM’s KL703 500w PEP Amplifier Test

  1. Robert Dixon says:

    Preamp failed in 3 months. It kills all signal if turned on now.

  2. Leave it turned off. They only ever increase the noise.
    I guess you were using the rx pre amp…how about sharing your thoughts. Did the pre amp help? Using the amp mobile or base?

  3. Jeff Holzer says:

    I got one running it on 16v have done for 6months… I also now use a RM KL60 to drive it. I’ve been told I’m one of the loudest stations in my city.
    Skip is like if I hear them 100% they’ll hear me..
    As for watts I wish I could send a pic of my power meter..
    If I told you, you wouldn’t believe me..

    • I am not surprised. A single kl203 could hit 200w pep but not sure all the watts were òn the same frequency! Or for very long. With this box 800 is not out of the question and the case and fans could easily handle the heat. And with 16 volts who knows? I assume we are taking AM here? It is one solid amp for sure.

  4. Robert Dixon says:

    I use a President M Kinley tuned to 6 Watts, or the CRT SS9900 radio adjusted to 8 Watts . 8 Watts is yielding aprox 300 W dead key.

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