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Author Topic: Need plans to build a solid-state HF amplifier  (Read 2945 times)
WB0AXN
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Posts: 90




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« on: March 20, 2003, 07:52:03 PM »

I've searched the web and am unable to find complete plans for building an HF solid-state amplifier using four 2879 transistors.  I need a schematic, parts list and pattern to make the printed circuit board.  I don't subscribe to QST or CQ magazines anymore and don't have any back issues.  

Has anyone reading these forums built a solid-state amp and can offer some tips & suggestions?  

TIA
Roland
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WB2WIK
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Posts: 20574




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« Reply #1 on: March 21, 2003, 02:58:31 PM »

You normally wouldn't find any good design using 4 x 2SC2879s on a single board; however, 2 x 2SC2879s are a common configuration and have been used in many popular HF amateur transceivers like the TS-440S, to run 100W PEP output.  So, two identical 2x modules could be combined to run 200W PEP output, and that's the way most people do it.

The Toshiba Application Note on the 2SC2879 contains circuit and biasing details, but leaves the PC board design up to you.

I greatly prefer sticking with Motorola transistors from the MRF4XX family for these applications because the Motorola Application Notes and Engineering Bulletins contain complete circuit board layouts and dimensions, and most of the boards are readily available already fabricated by Communication Concepts, very inexpensively.  Plus, to generate any serious power, I'd prefer to use higher voltage transistors (28V to 50V) instead of 14V transistors like the 2SC2879.  The lower voltage limits how much power is available while maintaining linearity.

If you didn't already buy the transistors, you might contact CCI and go with a Motorola-based design.

WB2WIK/6
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WB0AXN
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Posts: 90




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« Reply #2 on: March 21, 2003, 08:01:17 PM »

WB2WIK/6,

Your info is exactly what I wanted to see!  Thanks!
I'm guessing people use the 2879's cuz they are pretty cheap to buy.  I saw a homebrew amp at a hamfest a week ago, using two transistors.  It was on a board measuring 4" x 7", 3" high.  It didn't have any input and output filters, however.  

The reason I want to build a solid state amp is, they can be run on a car battery and 2amp charger.  I use a car battery and charger now to power my Icom rig.  

Another regular poster here sent me an email and suggested I use "tunnel FET's" instead of the 2879's.  Two FET's will produce 1000 watts and use a 12 volt battery and the FET's cost $50 each?  

Thanks again for your post and info therein....

Roland
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KD5VHF
Member

Posts: 84




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« Reply #3 on: March 22, 2003, 01:22:34 PM »

You might take a look here: http://users.aol.com/rfelectron/rfelect.htm There is some nice pic.s of one on this site. http://www.worth-more.com/
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KC8WBK
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Posts: 2




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« Reply #4 on: April 08, 2003, 04:53:58 PM »

http://www.hfprojects.com/projects.htm
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N0TONE
Member

Posts: 173




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« Reply #5 on: April 08, 2003, 06:44:15 PM »

I looked at the Worth-More page.  Very sad.  The photos of the amplifiers show mediocre build quality.  There's no shielding whatsoever betweent the PA stages and the filters (at least the amps have filters).  I'd bet these amps do not meet FCC specs for harmonics.

Also, it's scary to NOT see IMD specs.  Our crowded bands are in dreadful shape because of the amount of splattery-IMD products from poorly-built amps.  The fact this this website gives no specifications for spectral purity suggests that the spectral purity is poor.  He gets 300W from a pair of 2SC2879 devices.  Having done that myself, I can guarantee that the intermod is terrible - that's too much power from those transistors.  They will survive, no question, but they'll be generating "gook" many kHz wide.

Also, note that the amplifiers are all RF keyed.  That is prohibited by the FCC if an amp is going to be certificated.

His claim "Sales Pending FCC Type Acceptance" is pure fiction.  The FCC dropped the "Type Acceptance" nomenclature several years ago, replacing it with "certificated", and it's a new process.  And, with RF-activated keying, the FCC will NOT approve these amps.

It is fairly clear that he will accept orders today, in violation of FCC rules.

I would not buy one of these.

AM
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N6OTQ
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Posts: 6




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« Reply #6 on: July 11, 2003, 11:35:44 AM »

You won't find detailed plans because this particular design has been over-abused for CB amps.  If you need a schematic, try a google search on "CB linear."  There's plenty of info out there for performing CB tricks dot com.

IIRC, some of the Texas Star "QRP exciters" incorporate a PA board using this exact configuration.

Be aware of FCC regulations and their interpretation before you begin to build.

Jim N6OTQ
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W6KAN
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Posts: 11


WWW

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« Reply #7 on: August 02, 2005, 01:02:44 PM »

You can take a look at www.k0gkd.com/ssamp.html - it was a fun project and not very difficult once you get in the mood.

73's  Tom K0GKD
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W6KAN
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Posts: 11


WWW

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« Reply #8 on: August 24, 2005, 12:09:48 PM »

Roland...try www.k0gkd.com/ssamp.html
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