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Author Topic: Rookie Amplifier User with a Question  (Read 1829 times)
W9DEC
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Posts: 58




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« on: February 16, 2013, 02:06:09 PM »

I've decided to try an amp and I have a Ameritron ALs 600s on the way . I'm going to use it with a vertical  6BTV antenna. I'm wondering if I will need a tuner? My SWR readings are pretty good with most levels under 2.5 : 1. Will I need a tuner and if so what  recommendations would you have for my setup. The radio is a Kenwood 590s. Thanks in advance for your opinion.
73
W9DEC
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KE3WD
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Posts: 5689




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« Reply #1 on: February 16, 2013, 02:26:31 PM »

Most solid state amplifiers (and radios) will start to foldback the power output to protect the finals at around the 2:1 mark, some do it earlier. 

But my advice to you is to first see how bad the foldback may be and at what freqs before worrying about which tuner. 


73
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W5LZ
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Posts: 477




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« Reply #2 on: February 16, 2013, 03:27:38 PM »

And naturally, your best option would be to re-tune that antenna, or correct whatever other faults it may have.  But, sometimes that's not possible for whatever reason.  In that case, a nice tuner would certainly be handy.  Having 'played' with a lot of tuners over the years the best advice I can think of there would be to get a 'larger' one than you may think you need.  I don't mind 'twiddling' knobs so would recommend a manual tuner.  That's personal preference mainly, so it's up to you.
 - Paul

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K8AXW
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« Reply #3 on: February 16, 2013, 05:40:56 PM »

It would be nice if you could get the SWR down a bit more.  To me, 2.5:1 would be unacceptable!  I'm surprised your rig hasn't 'folded back' to a lower power setting.

Adding an amp isn't going to change anything, except for the better because the amp input should present something better than a 2.5:1.

Unless you have the money to spend on an automatic tuner that will handle 600w, try to find a manual tuner that will handle MORE power than the ALS-600.  Antenna tuner capability is like desk space.  You never have enough.
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WX2S
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« Reply #4 on: February 16, 2013, 05:57:40 PM »

I also have a 6BTV. SWR does get above 2:1 at band edges, which will limit the power you can operate the ALS-600 at. The manual recommends 2:1 maximum SWR, which is pretty much standard for solid-state amps. Tube amps can take a little more, at 3:1, which gives me all the bandwidth I need without an ATU.

The amp has protection against reflected power, which will help. An ATU will get you more bandwidth, at the cost of higher peak voltages in everything between the ATU and the antenna.

Also, even the best ATU will not give you the full 80M band with a 6BTV.

Spring for an AA-54 and tune the antenna to put the low-SWR band segments where you want them.

73,
- WX2S

« Last Edit: February 16, 2013, 05:59:41 PM by WX2S » Logged

73, - Steve WX2S.
I subscribe to the DX Code of Conduct. http://dx-code.org/
N6AJR
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Posts: 9927




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« Reply #5 on: February 18, 2013, 10:10:35 AM »

The out put is also dependent on how much power you feed the amp, so when operating  into higher swr, cut down on the power a bit. The amp will last a lot longer if you don't try to get every last ERG of power out of it all of the time.  They will never hear the difference between 500 and 600 watts on the other end.
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WB2WIK
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« Reply #6 on: February 18, 2013, 10:28:30 AM »

I have a 6BTV and have installed a lot of them.

They can be "adjusted" for SWR <2:1, using a proper radial system, for most of 10m, all of 15m, all of 20m, all of 30m (as narrow as that band is!), and almost all of 40m.  I set mine to "dip" to nearly 1:1 near the center of those band segments.  On 75/80m, it's another story altogether and can only cover about a 50 kHz slice of the band <2:1, if that.

So, if you use the antenna on 80m, a tuner will really be required unless you only operate in a very narrow segment of that band.

But on the other bands you really shouldn't need one, if you spend some time adjusting the antenna itself.

I'm using an elevated installation (base about 22' above ground) with "tuned" radials for each band, so mine has 20 radials attached (four per band, and using the 40m radials for 15m also) and after making the antenna adjustments, I "fine tuned" the whole system by adjusting radial lengths -- which does work.  With the radials sloping as they are (they slope about 20 degrees from antenna to ends), I achieved a 1:1 or very close to 1:1 SWR on a center frequency in every band.
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KR4BD
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« Reply #7 on: February 18, 2013, 10:37:43 AM »

I have had an ALS-600 for over a decade and use it with various antennas.  The amp will "kick out" anytime the SWR hits 2 to 1, or worse.  In your case, I think you will need a tuner capable of handling about 1KW to use the amp on band edges to keep it from kicking out.  I try to keep my SWR at 1.5 or less for BEST results. 

Tom, KR4BD
Lexington, KY
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W9DEC
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Posts: 58




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« Reply #8 on: February 20, 2013, 05:31:00 PM »

Today I returned the antenna to the original settins and then adjusted the traps and improved the SWR dramatically on all bands. I i istill have some work to do on 80, but the other bands are in good shape.
Thanks to all for the good advice and gentle nudge. Now when I add some power  I should get some good QSO's?
73
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WB2WIK
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Posts: 20666




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« Reply #9 on: February 20, 2013, 05:52:09 PM »

Sure, why not?

Although I do have beams for 20m and above that, I use my 6BTV on 30m often, and 40m about half the time (I have an inverted vee at 55' for the other half the time), and even "sometimes" on 80m (CW only, I tuned it for 3525).

Using 100W I've worked all over the world with it for years.

A lot of the "secret" is how good a radial system you have, of course.

I find the 6BTV to be a "killer" antenna on 40, it is as good as my 55' high full-sized inverted vee quite often, and sometimes better than that.  Worked Mali on 40m CW from here in CA a few days ago.
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