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Author Topic: 10 meter amp for 6 meters  (Read 9593 times)
K5MBV
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Posts: 265




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« on: December 05, 2008, 06:50:48 AM »

Has anyone had any sucess in modifyng a 10 meter or all band brick or tube type linear of 400W or more to 6 meters? I have a 100W FT-100D to use as a 6m driver.

I want to increase my power to 300W or more for meteor scatter, but can't afford an expensive 6 meter amplifier. There are a lot of inexpensive 10 meter (CB)
amplifiers on eBay that I could choose from if this approach would work.

Seems like some of the bricks should be broadband enough that with a little reduction in drive and output (plus a blower) they could be used for this
application.

I know about harmonics and spectral purity, but the all band bricks just use ferrite transformers to match
the in and outputs. The tube type amps typically use pi networks which are band pass and not low pass filters so there don't seem to be any limitations that
couldn't be overcome except for the active device frequency ratings.
Ken K5MBV
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KB9CRY
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« Reply #1 on: December 05, 2008, 10:55:16 AM »

Boy, one would think if it was easy to do, we'd all be doing it.
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N3JBH
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Posts: 2358




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« Reply #2 on: December 05, 2008, 11:20:08 AM »

Ken considering you could make the changes needed dont you think it be better to pick up an old sb-220 or some thing and mod that? I know the up front cost might be higher then coneverting Ole Bobby Browns 10-4 good buddy antenna smoker. But i think you be much happier with the end results. plus there all kind of info on it all over the net. And i bet others will jump in and offer some advice too....Jeff N3JBH
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K6AER
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« Reply #3 on: December 05, 2008, 11:23:16 AM »

Doing meter scatter on six meters is difficult at best even with the best of equipment. Under some ideal conditions you can have it happen with 100 watts and a dipole but it is rare.

Even under the best of conditions using 1500 watts, low loss coax and a 13 dBi gain antenna up high it is not easy. Your bang for the buck would be best concentrated on building a high gain antenna system first. All the power in the world will not help if the receiver is challenged by a low gain antenna and a high loss coax feed system.

Now on to your amplifier question. Most HF amplifiers do not have the device gain that will product much power above 30 MHz. Solid state amplifiers generally require a different device to go up one octave in frequency to six meters. You did not mention if you are going to do this with CW or SSB. If it is SSB the amplifier will have to be linear and not an FM class C device. If the mobile amplifier has a brick module for power output the power out is probably under 100 watts and is a class C device.

You can build a CCI module such as AR347 for 1000 watts out on 6 meters but the parts will run you about $800 and that will not include power supply, filters, chassis, and other components. This is not a project for the non amplifier first time builders

Tube amplifiers will provide much more power but again tube gain is a problem. Even a 3-500Z produce only 60-70% of its rated power at 50 MHz. Tubes such as 811 and 572’B’s produce little power at 50 MHz. VHF amplifiers almost always use ceramic tubes which have a much higher operating frequency. Tubs such as the 8877, 3CX800A7 and 4CX800A7 are popular tubes.

If you do want to run power on 6 meters and are not comfortable with building your own, I suggest you buy a ready made amplifier such as a Lunar, Commander, Tokyo High Power or a used Henry amplifier. Some Heathkit SB-220’s have been modified for 6 meters and you can find them at large swap meets such as Dayton.
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K6AER
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« Reply #4 on: December 05, 2008, 11:59:09 AM »

Correction, the CCI module such as AR347 will cost up to $1200. I had not known the price on the MRF-154 transistors had gone up so much in cost.
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K5MBV
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Posts: 265




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« Reply #5 on: December 05, 2008, 12:31:12 PM »

I believe I mentioned using an ALL BAND brick, so
the statement: "I know the up front cost might be higher then coneverting Ole Bobby Browns 10-4 good buddy antenna smoker. But i think you be much happier with the end results." doesn't apply to that.

Yeah,the 10 meter only amp isn't such a good idea, although I would expect it could work depending on the design. That's why I asked.

I really don't want to have to use a narrow beamwidth
yagi. That's why I want to use a 3 el instead of a 35
or 40' monster that would hang up in one of my trees anyway. I would depend on the other station to have a
higher gain antenna and both of us running some power.
If this doesn't make sense, I could order another 3 el and stack them, but I don't expect that all meteor trails will be right down on the horizon and they should appear to trail in slightly different directions. Is this incorrect?
Ken  K5MBV
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K5MBV
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Posts: 265




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« Reply #6 on: December 05, 2008, 12:38:24 PM »

The first one of the amps I saw mentioned here was the Lunar. I googled this and found that they never built a 50MHz amplifier. Just 2 meters and up.

High power 6m amps are hard to find.

Ken  K5MBV
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WB2WIK
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Posts: 21837




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« Reply #7 on: December 05, 2008, 12:54:57 PM »

>RE: 10 meter amp for 6 meters       Reply
by K5MBV on December 5, 2008    Mail this to a friend!
I believe I mentioned using an ALL BAND brick, so
the statement: "I know the up front cost might be higher then coneverting Ole Bobby Browns 10-4 good buddy antenna smoker. But i think you be much happier with the end results." doesn't apply to that.

Yeah,the 10 meter only amp isn't such a good idea, although I would expect it could work depending on the design. That's why I asked.<

::Legitimate 10m amps, or "all band HF" amps that were not designed to cover 6m from the start, usually cannot achieve any output at all on six meters because they have a LPF with a cutoff frequency of 32 MHz following the PA stage, to keep them legal with regard to harmonic content on the 21, 24 and 28 MHz bands.

>I really don't want to have to use a narrow beamwidth
yagi. That's why I want to use a 3 el instead of a 35
or 40' monster that would hang up in one of my trees anyway. I would depend on the other station to have a
higher gain antenna and both of us running some power.
If this doesn't make sense, I could order another 3 el and stack them, but I don't expect that all meteor trails will be right down on the horizon and they should appear to trail in slightly different directions. Is this incorrect?<

::It's mostly incorrect.  The meteor trails you want to be working are right at the horizon, otherwise there's not much advantage in working them: If they were "overhead," not only could you never get a signal up to them, but any reflection that's useful to make a contact would come down where you already are and you don't need the meteor trail to do any work.  I've always found large, high-gain and thus (obviously) very narrow beamwidth systems work best for meteor scatter.  Probably the best m.s. antenna system I ever had up at home for six meters was my 20 element stacked array of four 5-element Yagis in an H-frame: Its forward gain was about 17 dBd and that was focused right on the horizon.  Worked m.s. 365 days a year with that, it didn't take a shower or storm to do it.

WB2WIK/6
 
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K5MBV
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Posts: 265




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« Reply #8 on: December 05, 2008, 02:10:36 PM »

HI WB2WIK/6  

Thats the kind of information I was looking for. I'll
be unable to put up a big antenna, but I will order another 3 el and stack them. That's the best I can do for now without cutting a tree down and my wife doesn't want that. You had a real monster of an antenna! I have had only one sked of ms and the copy
was good using wsjt. I couldn't transmit yet due to no
interface. The new SignaLink seems to be just fine and I'm looking forward to ms on 6m.

Ken  K5MBV
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WB2WIK
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Posts: 21837




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« Reply #9 on: December 05, 2008, 02:23:42 PM »

Hi Ken,

I'm an "old timer" for m.s. and did 99% of my meteor scatter work using SSB or CW -- actually, mostly SSB because "anybody" can copy that, even if they stink at code.

To work scatter via SSB causes one to develop very crisp diction and very fast speech.  I can speak about 150 words per minute very clearly and distinctly after all those years of scatter practice.  A 2-second burst can thus allow a nearly complete "contact," if the other operator is similarly skilled.  This was all WAY back in the day before WSJT, and before anybody even had a home computer.

Most of my really active 50 MHz m.s. work was done c.1969-1987.   The "later" days we had computers, of course, but WSJT hadn't been developed yet and really nobody was using computers to do anything with meteor scatter (yet).

Home station setup at West Long Branch, NJ (QTH from 1986 to 1988, until I moved to CA) was:

TS-830S on 28 MHz
Microwave Modules MMT50/28S transverter
Homebrew grid-driven 4-1000A, 1.5kW PEP output
Advanced Receiver Research GaAsFET masthead preamp
140' 1/2" Heliax to four stacked 5 element beams at 72'

Took the entire setup, including the four beams, to Chincoteague Island, VA (FM27) for the June 1987 VHF QSO Party, where we set up as WB2WIK/4 (multiop).  Worked 204 grids, 50 states, 13 countries in 36 hours over one weekend on 50 MHz from there, giving about 700 operators their "first FM27."

That was fun.

:-)

WB2WIK/6
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K5MBV
Member

Posts: 265




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« Reply #10 on: December 05, 2008, 05:24:28 PM »

That's awesome! 13 countries! With the beams and that
feedline, did you really need that preamp?

I'm using the same brand on 2m and 70cm and they work
fine, but I'm not sure they make a difference. I'm using 1/2" heliax on both bands, but the run is only 60'or so. They are my satellite antennas so they
aren't but 30' high. The 2 meter beam was about 48' long until I cut off about 15'. Yes it did change the SWR.
The computer controls the az and el. Just not much interesting going on with the sats nowdays. Waiting for the new German bird to get a
launch.

Ken
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WB2WIK
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Posts: 21837




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« Reply #11 on: December 05, 2008, 06:30:08 PM »

I used the preamp to overcome the loss of 140' of feedline, and it helped slightly.

13 countries was no big deal at all; more impressive is that as far as I know (unconfirmed) we were the only station to ever work all states (50) in the course of one single weekend on 50 MHz.  The ARRL advised us at the time that was never done before; it may have been done "since," I don't know.

WB2WIK/6
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W1QJ
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Posts: 2984




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« Reply #12 on: December 06, 2008, 05:25:46 AM »

Just wanted to say that it is a bunch of HOGWASH that a 3-500Z tube only makes 60-70% of its power on 6 meters.  The tube will perform just as well on 6 meters as it will on 80 meters.  
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K6AER
Member

Posts: 5745




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« Reply #13 on: December 08, 2008, 09:05:42 PM »

I should have been clearer.

The problem is not specifically the tube which is good to 110 MHz but in the typical amplifier conversion. Typical 3-500Z amplifiers, SB-220 and such, that are converted to 6 meters have more stray inductance and as a result the power output is lower due to loses. With the longer leads in the construction of the 3-500Z the efficiency is lower, and needs more drive.

Add two tubes and the problem gets worse. You could build a 6 meter only amplifier using the 3-500Z but if you are going to build a ground up 6 meter amplifier why not use a better tube such as the 3CX800A7 or an 8877 or possibly the Russian GU-35B.
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W1QJ
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Posts: 2984




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« Reply #14 on: December 09, 2008, 01:50:13 PM »

K6EAR, an Sb-220 converted to 6 meters properly as a single band 6 meter amp will easily do several hundred more watts output on 6 meters as it will as an HF amp on 80 meters as it was constructed by Heathkit.  MY 6 meter SB-220 conversions perform extreamly well on 6 meters and easily outperform the Sb-220 as it was originally designed.  Check out my King Conversions reviews here on EHAM.  73 Lou
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