An alternative to expensive solid-state amps?

1kwA look at the prices of Elecraft’s KPA-500 ($2500) and various other solid-state amps from Tokyo Hy-Power (up to $7300), Expert (up to $8000) and even Ameritron will make one quickly realize why tube amps remain popular despite the inconvenience of needing to be tuned for each band QSY.

If you don’t mind ugly construction, the need for a 48-volt DC power supply and a lack of band filters (easily solved – we are hams after all) and the lack of various safety circuits then there may be an alternative.

And, if his feedback is any indication, not a bad alternative at all – though I suspect much of his feedback is from CB’ers, thus the lack of switchable band filters.

Baruch 4Z4RB builds some of his amps based on Motorola designs sold as kits by CCI. I’ve builtspec_an one myself and can vouch for the 140-watt EB63 as doing what the ads say it will.

Based on my experience with the EB63 I’ve been tempted to build something from CCI with a bit more oomph but the show-stopper has been that, whereas the EB63 has a carrier-operated relay that handled T/R switching, the higher power amp kits do not.

That added complication dampened my enthusiasm for experimenting with the higher power – and therefore higher dollar – amps.

Check out Baruch’s eBay store here – and understand that I’m mentioning – not necessarily recommending!

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  8 comments for “An alternative to expensive solid-state amps?

  1. December 7, 2013 at 1:23 pm

    High power amplifiers are much more than a bunch of parts put together. Even though the Motorola application notes are a good start for a good amplifier, there is alot more work involved in developing protection circuitry (wich is not optional, NEEDS to be there) , low loss efficient output filtering and especially proper cooling. I have played with MRF-150’s and I can tell you they can be tough as nails or blow in an instant depending on the working conditions (voltages, temperature, SWR).

    I have been looking ad Baruch’s work for some time, he seems to know what he’s doing BUT: the build quality seems very sloppy and I have only seen opinions of unsatisfied customers so far.

    Razvan YO9IRF

    • December 7, 2013 at 2:42 pm

      Hi Razvan – yes there is much more to a SS amp than the “pallet” as it’s often called. Like you, I have been looking at Baruch’s amps for a while now too and have the same opinion of them you do (though his feedback on eBay seems very positive). I eventually came to think of them, not as finished products, but as starting points. Then I found a few other builders of these CCI/Motorola amps (linked above) to see what features other builders incorporated into their designs.

      I think there is a YahooGroup for builders of the 600W model but I haven’t checked yet to see how current it is. The benefit of such a group is that, over time, the accumulated knowledge of several builders may now allow one to build an amp that’s more stable and reliable than any finished product on eBay.

  2. December 7, 2013 at 1:32 pm

    There’s also this project:

    http://www.jumaradio.com/juma-pa1000/

    It looks promising and I had high hopes about two years ago but the project makes slow progress or at least there is little news and long time between updates…

    • December 7, 2013 at 2:47 pm

      I keep hearing conflicting reports of Juma. They caught my eye several years ago with their QRP rigs and recently I read that they (and other Juma items) were no longer available in any timeframe that exists within a human lifespan. I like the idea of a kit amp – even if it were for tubes – and don’t know why there aren’t any. I think if Ameritron amps were offered as kits, they’d sell Big Time – just like the old Heath SB-220’s did. But that’s another topic…

      Thanks for the heads-up on this one from Juma. I’ll keep an eye out for further news from them.

  3. December 7, 2013 at 3:47 pm

    The EB-104 project is fine and can be reproduced, Communication Concepts sells kits. BUT, alot of people complain about the mosfets blowing, because proper protection is hard to get right without alot of R&D.

    As for the Juma amplifier, it is basically a failed project as the heart of it – the Freescale MRFE6VP61K25 – is a LDMOS mosfet pair made for VHF/UHF class C and/or impulse work, and proved not fit for HF linear work. Not even with huge standby currents it doesn’t stay in the linear region past half the rated power output, and the harmonic products are impossible to work with – even the manufacturer says -7dBc for the 3rd harmonic, but experimenters observed even worse. There’s a topic on the Juma forum about it, also look for the observations of W4YN and 5B4AGN testing the Freescale LDMOS. Some Italian manufacturer announced a HF linear based on the MRFE6VP61K25 too last year, but it seems it won’t make it to market either.

    I’m curious how Baruch is testing those kits in these conditions, he also has products based on the Freescale LDMOS.

  4. December 7, 2013 at 4:40 pm

    Speaking of solid-state amps, here’s a new one for QRPers:
    http://www.kightradio.com/MX-P50A-FT-817-QRP-HF-AMPLIFIER_p_315.html

  5. Yuli 4X6HP
    April 6, 2014 at 4:08 am

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