Thursday, April 27, 2017

Legal-limit solid state amps compared

With both Elecraft and Flex now adding solid state 1500 watt amplifiers to their line-up I thought it would be interesting to compare some of their main features with each other and with two other amps.



Each of the amps compared here have unique features that deserve attention. Further information can be found at:

Elecraft KPA1500
Flex PowerGenius XL
RF Kit RF-2K+ and the YahooGroup (manual, photos, etc)
SPE Expert 1.3K-FA

I'm happy to see a kit being offered in the QRO category - long overdue IMO. I've long thought that a KW tube amp would have made for a popular commercial kit but now that technology is moving from glass to MOSFETs, I hope the RF2k+ does well.
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10 comments:

  1. I can't tell if the RF Kit RF-2K+ includes a low-pass filter (LPF) on the output. That is required for operation in the US. That is a broadband amp, so the harmonics will be above what is allowed.

    The web page says the kit LPF will be available Spring 2017. The LPF section is usually fairly expensive, because it requires a lot of high-power toroids and capacitors. I'd use the ATU pricing as a first guess.

    That would bring the kit price up to about $3000.

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  2. I don't think the SPE Expert 1.3K is a 100% duty cycle amp. Here is a quote from page 32 in the manual:

    "RTTY: Digital modes, SSTV and FM, because all these mode have a very heavy duty cycle, you should not operate in “MAX”. It is best to use the “MID” or “LOW” power settings."

    "AM: This transmission mode radiates a continuous carrier which is 25% of its PEP value (e.g. 400W PEP AM = 100W carrier power). SPE recommends you always operate in ‘MID’ or “LOW” mode for AM."

    Page 33:

    "ATTENTION: Never stress the amplifier with long periods in key-down transmission, as this can stress the amplifier components. However, sophisticated Soft Ware avoids transmitting a continuous signal in the "MAX" condition for long periods by switching to "MID" power."

    MID is 800 W, LOW is 450 W (page 53). The main page data sheet says LOW is 500W.

    http://www.expertlinears.com/pdfs/expert_1-3K_manual.pdf

    K6WRU

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    1. You're absolutely right! I've modified the chart and am trying to find now where I (mis)-read the duty cycle when I made the chart. Thanks.

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    2. I can confirm that the 1.3K-FA is not a 100% duty cycle amp. It may work for a weekend on SSB or CW contesting at 1300-1400w but during RTTY contesting after a few minutes it will alarm and drop back to MID power level (800w). It is a nice, small, light amp but it should not be marketed as a legal limit amp, at least not in the US. They are really pushing the spec here. Also the 50W drive is the US spec model. Non-US model requires as little as 8 watts. - N2RJ

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  3. Even with the LPF, the amp would be illegal in the US due to having in excess of our 15 dB gain limit. This amp had 30 dB of gain (1.5 watts in, 1500 watts out) but as a kit it may not fall under that rule.

    I emailed Reinhard a few days ago but didn't ask about the filter availability. I am not in the market for a legal-limit amp but if I were, the relay T/R switching would have me going for the SPE amp instead. Still, I like to see that such a kit does exist and wish there were some other options out there.

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    1. If you import an amplifier yourself, kit or fully assembled, for your own personal use, it is legal. The 15dB gain rule only applies to amplifiers offered commercially for sale. - N2RJ

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  4. Kits can exceed the 15 dB limit. That rule is for manufacturers. Amateurs are allowed to build their own equipment.

    You could even modify an off the shelf amp to increase the gain.

    K6WRU

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  5. Hi from Reinhard,
    I’m DH3NAB the guy who developed the Kit.
    Thank you John for comparing the Rf2K+ Kit with the commercial amplifier.
    This is a Kit and I by now way would like to compete with the commercial player.
    Even we have some features which none of the commercial players has, this amp is from HAM for HAM’s.
    I’m with your comments, that it was overdue to get a Kit like this out for ever OM who would like to some hands-on building his station.

    The mentioned price is including LPF as nobody should run an amp without.
    Guess some do. Hi


    If you are in Dayton, please step by at Booth 6506 and we can talk about and get your questions answered.

    Vxy73 de DH3NAB

    Reinhard

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    1. Thanks for the comment, Reinhard and for answering my questions via email. Whether you intend to compete with commercial manufacturers or not, the price of the RF2k+ makes it a worthy consideration for those who want to build their own or who want a high-power amp without spending 5000-7000 dollars.

      As a CW op, my question about T/R delay has to do with whether or not the relays would chatter at a CW speed of 25 wpm or is that fast enough that the relays would remain in the TX position and not cycle T/R states between characters? An adjustable delay would let users tailor the delay to their own preference. Not an issue on SSB or other modes, but on CW it is.

      Thanks again and maybe see you in Dayton,

      John AE5X

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    2. Tim O'Rourke W4YNApril 30, 2017 at 7:28 AM

      I have built this amp and am impressed every time I fire it up!
      As Reinhard said it is a kit for amateurs, and I would add that it is for those who have some build experience behind them. It is not difficult however you need be careful while setting it up and follow instructions. There are several builders on the Yahoo forum who will help with assembly and setup questions. This is a great amp, the touch screen and menus make operating and setup very easy. Tim W4YN

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