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Author Topic: QRP HF Power Amp  (Read 22571 times)

Posts: 66


« on: February 21, 2001, 01:02:36 AM »

I would like to use my FT-817 mobile on HF and think 5 watts may not be enough? Are any suitable commercial HF PA's available? I would think 50 watts would be about right.

Or . . . is anyone running 5 watts mobile with success? I have had luck running 30 watts on 10-meters, but don't know about the other bands.

Thanks! joel Sampson / N5LXI

Posts: 18466

« Reply #1 on: February 22, 2001, 04:07:23 PM »

You might look for an old Ten-Tec 405 linear amp, which was
sold along with the Argonaut.  2 watts input, 50 watts output,
covered 10/15/20/40/80, but was basically broadband, so probably
could be used on the WARC bands as well.

The main reason you don't seem such things produced
commercially these days is that the FCC rules don't allow them.
This was done to keep them from being used on CB radios.  Since
the ban was implemented before QRP became really popular, there
are relatively few such amps produced when they were legal.  (But
there are still a number of illegal CB amps around...)

Or, if you find an old junked Yaesu FT301, they came in two models
(QRP and QRO), and the difference was an amplifier box on the
back panel.

But you may have to build your own.  Check the CCI adds in QST
and their web page, and perhaps RF Parts - they carry the amp
kits designed from the Motorola tech notes, and one of them may
work for you.

5 watts mobile?  Probably will work a lot better on the higher bands,
where mobile antennas are more efficient, like 20 - 10m.  Signals
will be much worse on 80, for example, where good mobile antennas
are only 10% efficient.

Posts: 149


« Reply #2 on: February 24, 2001, 03:14:10 AM »

The folks at Ramsey make a 20 Meter amp with about 20 watts out.
Folks think it is good stuff with a bit of tweaking.
Do a keyword search with Ramsey and 20 meters or amplifier.
Hope this helps.

Posts: 21837

« Reply #3 on: February 27, 2001, 01:27:31 PM »

I have a suggestion as well: You might consider the Communications Concepts Inc. (CCI) model EB-63 amplifier kit.  It's great "bang for the buck," costing only about $100 or so including the amplifier printed circuit board, a kit of all the electronic parts, and complete instructions.  This is not a "Heathkit" type kit, where all you need to know is the English language, it's a bit more difficult than that.  It's based on a Motorola engineering bulletin (#EB-63, hence the model name) and it works very well.  5W drive produces about 100W output (possibly more) on 3.5 through 30 MHz bands.  The kit is not complete, to the extent that you have to supply your own chassis and heatsink, and maybe some other easy-to-find components (on/off switch; cooling fan, if necessary; in-line fuseholder -- stuff like that), which frankly are all at Radio Shack.  I built one back in 1989, and it's been plugging along reliably for the past 12 years with zero problems or failures.  It probably does NOT meet the spectral purity requirements for HF commercial equipment, without adding output filtering; however, I've found it is extremely clean when operated in its LINEAR range (not in compression!), and that does extend up to about 100W output power.  And the cost is hard to beat.  Also, if you build it yourself, you'll definitely know how to service it, should that requirement ever occur.  I've been using mine mobile/portable for years, never a problem, never a complaint.  It draws about 15A peak at 13.8Vdc for 100W output power.  Good luck!

Posts: 14

« Reply #4 on: July 05, 2001, 10:59:55 AM »

I found that mobile power out is not as much a problem as rx noise floor.  I work all kinds of dx with 5w cw. Whips lend themselves to that low angle radiation for the dx.  I don't think you would do well trying to get into nets, or local scheds though.  That 100W kit mentioned might be the ticket for that kind of operating.

Posts: 2

« Reply #5 on: December 05, 2001, 08:18:08 AM »

Here in Germany you can get broadband PA's from different manufacturers which are specified for 3-30 MHz use for approx. 100 US$.

In case I can go mobile or portable and I don't have a power supply challenge, I am running my FT 817 with a ZETAGI B300P which is ....hmmmm.... supposed to have 300W output at 10 W input.  I get something like 130-140 W output. Reports about modulation in SSB are fine, so the linearity seems to be not too bad. I usually have connected a 30 MHz low pass filter, as well as a homebrew Pi-filter tuner. This should avoid the worst harmonics problems, but I am still working on my winter project which is a multiband lowpass filter.

Posts: 84

« Reply #6 on: December 26, 2001, 12:07:42 PM »

Hi.  There is a low cost source of HF broadband amps in old marine HF radios. At a local hamfest I bought 3 for $50.00 and all worked.  The PA is usualy a module attached to the heatsink with 100 mw to 1 watt required to drive the unit to full output ( Around 100 W.).  They usually work from 1.8 to at least 25 - 30 Mhz.  Mine were built by ITT Mackay, SEA and Intek.  Add a tr relay and enclosure and your ready to go on the cheap!  Lo pass filter parts or the whole filter is already there.  Just check inside and make sure they have not taken a salt water bath before you buy.  Look for xtal controled or PROM programed models as they will fetch the least $$$.  All we are interested in is the PA.

Randy KB8ASO

p.s.  Don't feel bad junking the marine radio as most are USB/CW only and usually do not go higher than 13.5 ish Mhz.  If yours is USB/LSB and doesn't use xtals or some funky PROM to program the freq's, DON'T junk it.  Use it!  These rigs are very stable and usually built to a high level of quality and reliability.  

Posts: 98

« Reply #7 on: January 20, 2002, 03:38:55 PM »


Posts: 55

« Reply #8 on: February 03, 2002, 04:18:56 PM »

The german company Wimo sells a 12 vols DC PA for Elecraft K2, FT-817 etc.
Switchable 50 / 100 watts out for 5 w in.
Available from end November 2001 according to the web.
I have not tested it, but it looks promising.
The only price info is from a ham journal in neighbouring Denmark; approx 240 dollars.
Have fun.

Posts: 26

« Reply #9 on: February 03, 2002, 06:39:07 PM »

I picked up a Tokyo Hi Power amp right here on Eham classifieds for about $225.  Covers 80M to 10M and will give between 40 and 50 watts out with 5 watts drive (it is designed for 10W drive).  With a simple mod it will give a full 60 to 65 watts out with 5 watts drive.  Nice modern compact amp.  Sometimes see them for sale on the HF pack or FT-817 group over on
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