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Author Topic: HF plus 6m amps?  (Read 2475 times)
NZ5N
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« on: February 23, 2009, 07:35:53 AM »

The only amps of which I am aware that cover HF plus 6 meters are the ACOM 1000, the Expert 1K-FA (Italy), the HA8UG Amplitec line, and the Tokyo HP HL-1.5KFX.  Are there any others?  Now that most HF transceivers include 6m, is there a reason why more amp manufacturers are not following suit?  Or are there technical reasons why this is not a good combo?  I have seen and heard the ACOM and the THP on 6m and they both seem to work well.

Thanks for any info and 73,
Bill NZ5N
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W1QJ
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« Reply #1 on: February 23, 2009, 07:45:51 AM »

Yes there is a technical reason why you don't see many multiband amps including 6 meters. The reason is mainly due to the fact that a load or tune variable cap that will be necessary for 160 or 80 meters will have too much minimum capacitance to work on 6 meters.  The Acom I believe switches in more variable capacitance to overcome the minimum issue,this increases cost.  Also with the losses in bandswitch etc with a multiband amp, you can not get a good Q to a coil for 6 meters in a multiband amp.  Though the Acom does work on 6, it is not as good as having a single band 6 meter amp,there simply is NO substitute for a single band amp, especailly on 6 meters.  With solid state broadband amps, this is not an issue.  That is why you see 6 meters on most solid state amps but not on tube amps.
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KB1NXE
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« Reply #2 on: February 23, 2009, 07:50:50 AM »

Add the Icom PW-1 to the list.
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WB2WIK
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« Reply #3 on: February 23, 2009, 08:31:16 AM »

The Icom PW-1 and Yaesu Quadra VL-1000 both also cover HF+6 meters.

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N3JBH
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« Reply #4 on: February 23, 2009, 10:28:43 AM »

http://www.kingconversions.com/

There ya go Lou build him a amp
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K5MBV
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« Reply #5 on: February 23, 2009, 04:11:02 PM »

Lou at http://www.kingconversions.com/ can build
an amp from an SB220 that will put out more than 1400W.
The price is right too.
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K5MBV
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« Reply #6 on: February 23, 2009, 04:11:29 PM »

Lou at http://www.kingconversions.com/ can build
an amp from an SB220 that will put out more than 1400W.
The price is right too.
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VR2AX
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« Reply #7 on: February 24, 2009, 04:27:35 AM »

Re the Acom 1000, this is what the RF section looks like in close up (scroll down)

http://www.vinecom.co.uk/ACOM1K.html

In contrast, this is what the single band Acom 1006 6m amp looks like

http://www.hfpower.com/new/images/1006_top.jpg

I understand the Acom 1000 is still reasonably efficient on 6m, viewed in its context as a 160-6m wideband amp.
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NZ5N
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« Reply #8 on: February 24, 2009, 05:43:32 AM »

Thanks for the replies.  Wyn, very interesting pics, the 1006 looks almost empty in the RF section.

ACOM must have come up with an interesting way of switching in the variable capacitance for 6m in the 1000 (note that the ACOM 2000 does not work on 6).  If it were easy, I'm sure that Lou and the other conversion specialists would have come up with a way to duplicate the ACOM system and sell an HF plus 6 version of the SB-220 and other old HF amps.

Sure, the HF plus 6 approach is "not as good" as a single band amp, but there would be a market for an amp that works on HF and provides even half power on 6.  Beats having an extra large, heavy box in a crowded shack.  I'm now using a converted AL-80B on 6 and would love to save the space.

73, Bill NZ5N    
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VR2AX
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« Reply #9 on: February 24, 2009, 06:03:49 AM »

Bill, there are lots of amps coming out of EU now, including:

http://www.reimesch.de/alpin200_en.html

I will leave Lou to explain why a single 4cx800 may tune up on 6m, whereas a pair may not.

73,
Wyn, VR2AX
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W1QJ
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« Reply #10 on: February 24, 2009, 06:39:21 AM »

The Q of a tank circuit on a multiband amp increases as you go higher in frequency.  Look at ANY multiband amp and you will see that it does not load up as smoothly or as easily on 10 meters as it does on 80 or 40 meters.  The "sweet spots" in tuning are a lot sharper on 10 meters than on 40 meters and the  bandwidth is also much smaller.  This is all due to the increased Q of the tank circuit.  This problem is even more pronounced if you add 6 meters to an HF amp!!  If you look at the photo of the single 6 meter Acom amp above, you will notice the very small amount of Tune "C" in the tune cap.  It's very small, about 15pf or less.  Most HF amps have a tune cap with a minimum "C" about 50PF, almost 3 times what is needed for 6 meters.  This is one reason why you don't see 6 meters on an HF amp unless "somehow" the minimum"C" can be reduced on the plate tune cap.  In my opinion, as far as "tube" 6 meter amps go, you can't beat a single mono band 6 meter amp.  As I said before, with wideband Solid state amps, this is not a problem, the problem there is end stage filtering.  I never worked with a pair of 4CX800's on 6 meters, but I don't see why a pair would not work on 6.  The 4CX800 is basically a tetrode form of the 3CX800 triode that a pir will work on 6 meters.  Naturally, the unltimate 6 meter amp will be an 8877.  I have converted many Ameritron Al-1500 amps to 6 meters, lets say you'll have about 800 watts of "headroom" over legal limit.  Not bad eh?
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NZ5N
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« Reply #11 on: February 25, 2009, 09:39:24 AM »

Lou,

What you say makes sense.  It's not possible to have a completely separate tank circuit for 6m that could somehow be switched back and forth with the regular HF tank circuitry?  That must be what the ACOM 1000 has.  You would surely be able to sell a lot more amps if you didn't have to remove the HF tank to do the 6m conversion.  There's only a limited market of hams who are willing to pay for a 6m-only amp, as the band is dead 90% of the time.  Obviously a stand-alone 6m amp is the best way to go, but an HF plus 6 unit would be popular.  

73, Bill NZ5N
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W1QJ
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« Reply #12 on: February 25, 2009, 04:38:56 PM »

Bill, no doubt an all encompassing 160-6 meter tube powerhouse amp will be the ticket!  And yes, one would be popular for sure.  I've looked at the Acom with 6 meters and HF, and they have a dual section tune cap, one section is about 5-20pf and the other is about 50-250pf.  They combine the 2 for lower bands and using only the small section for 6 meters, they switch it somehow.  Not sure how well it works, but I am sure it "works".  True, many don;t want to fork out for a seperate 6 meter amp, but how many hams have mono-band beams?Huh  Mono-band antennas are big bucks, but the BIG GUNS have them.  The BIG GUNS on 6 meters have mono band amps!!  I am busy enough doing them.  Hi Hi
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