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Author Topic: HF amplifier for FT8  (Read 1689 times)
VE2WFB
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Posts: 38




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« on: April 09, 2019, 11:53:13 AM »

Hi,

I would like to buy a good 160m to 6m HF amplifier to help me reach rare DX with FT8. I'm Canadian and Advanced Qualification allow us to use 750 W carrier power. I would like to be able to use max power for, may be, 5 to 10 minutes (15sec ON, 15sec OFF) without worrying about breaking anything.

Could you please tell me, according to you, what is:
1- the ultimate amplifier for this task (without worrying about $$$)?
2- the smartest choice i.e. price vs performance

Thanks in advance to share your knowledge with me!
73, Fred VE2WFB

Note: I'm using a IC7300 radio
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AA4PB
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Posts: 15018




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« Reply #1 on: April 09, 2019, 12:18:07 PM »

I'm using the Elecraft KPA500 for 6M FT8. I haven't pushed it above 400W, but at that power it will run 15 sec tx / 15 sec rx all day long. The front panel heat sink temperature display shows that the temperature stabilizes well below maximum for that duty cycle. If you really want to run 750W then consider the Elecraft KPA1500. It'll probably run 750W output all day at the FT8 duty cycle.

In either case, you can also save a few dollars by getting the kit version. It's a pretty simple mechanical assembly. Just mount the PC boards and plug in the interconnecting cables. All the cards are factory assembled, tested, and aligned.
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Bob  AA4PB
Garrisonville, VA
K6AER
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Posts: 5689




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« Reply #2 on: April 09, 2019, 05:05:02 PM »

Any amplifier you use must be capable of 100% duty cycle at your desired output. The question at this point is how much power is enough and do you want SS or tube amp. Lots of great bargains out there with tube amplifiers. Alpha 91B or a 99 will do 1200 watts all day long with 35 watts drive and have a very good IMD spec. This will take a big heat load off of the XCVR.

Sic meter coverage is going to add to the price or confine you to some of the SS offerings.

Also look at the OM-2000+ and OM-2000A.
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N9AOP
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Posts: 1150




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« Reply #3 on: April 10, 2019, 06:12:29 AM »

I prefer ACOM.  Both the 1000 and 2100 will run key down until your electric bill goes up.
Art
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VE2WFB
Member

Posts: 38




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« Reply #4 on: April 11, 2019, 05:47:25 AM »

Thanks all of you for you kind answer! As a new ham, it helps me a lot to start to know good company and model before buying anything. All info/feedback is very appreciated.
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K6BRN
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Posts: 1267




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« Reply #5 on: April 12, 2019, 06:03:26 PM »

Hi Fred (VE2WFB):

Quote
I would like to buy a good 160m to 6m HF amplifier to help me reach rare DX with FT8. I'm Canadian and Advanced Qualification allow us to use 750 W carrier power. I would like to be able to use max power for, may be, 5 to 10 minutes (15sec ON, 15sec OFF) without worrying about breaking anything.  Could you please tell me, according to you, what is:

1- the ultimate amplifier for this task (without worrying about $$$)?
2- the smartest choice i.e. price vs performance

Best/smartest is always subjective and affected by means ($), ability and expectations.  So... I offer some opinions rather than absolutes.

First, as you move above 500-750 watts output, you will need to make sure your amplifier, antenna and coax cable can ALL handle that sustained AVERAGE power level,  Pay ZERO attention to "ICAS" ratings for power whose meaning should be:  "In Credibly Absurd Speculation (ICAS)"   It is meaningless.  Ask about AVERAGE power, instead.

Many, many antennas (particularly those with baluns, matching transformers and traps)  are NOT rated to handle 600+ watts of sustained, average power.  End-fed wire antennas with a 49:1 matching transformer (transformer will overheat and go nuclear), Yagi beam antennas (even BIG ones) (traps will arc)... etc.  So... LOOK and ASK before you buy.

Thin coax cable with thin dielectric and conductors should be avoided.  Period.  It will heat and it's insulation may break down under voltage stress if the amplifier to antenna match (SWR) is less than VERY good.  And it's pretty flimsy to begin with.  Instead, use a good quality RG-213 type coax (Davis Bury-Flex and LMR-400UF are two good choices, as well as plain old RG-213).  Pay ZERO attention to destitute forum denizens who will argue that you can get by with wet string, RG-58 CB quality junk or even RG-8x.  Spend the extra CENTS PER FOOT to get something that will simply work and will not be easily damaged.  Or blow up your amp when it opens up or shorts out. (THATS THE REAL COST)

OK... about amps.  There are  cheap ones and there are quality ones.  Within limits, quality provides the better value, IMHO.  Cheap and unreliable is NOT for me.  Then there are 600 watts and under amps and 600 watts and over amps.  And there are tube amps (now fading from the scene, with consumable replacement parts - tubes - becoming scarce) and solid-state, no-tune amps.  I prefer the latter.

So, in that range....

The Elecraft KPA-500/KAT-500 five hundred watt amplifier/tuner combo is just hard to beat.  Works with just about every radio, with or without CAT control, no tuning needed (as in tube amp tank tuning).  This combo is overbuilt and easily handles FT8 at 500 watts out.  Runs off of 120 or 240 VAC, and is VERY compact, too.  About $2700 - slightly less in "no solder" kit form, slightly more assembled and tested, for the pair.  For your application, this is probably the best value, by far.  It's within 1.8 dB (less than half an "S-Unit") of your max power limit.  It WILL get you where you need to go.  I have one of these (as well as two other amps, one in the 600W range and one in the 1200 W range) and it is a gem.  Which is why resale value is so very high for them.  DO get the antenna tuner (KAT-500) with it.

For "No Holds Barred", the Elecraft KPA-1500 with built-in antenna tuner is a great way to go.  At $6,000, it's pretty pricey.  Runs ONLY on 240VAC.  Pretty compact (power supply can be separated from amp chassis).  Think of it as an industrial grade bulldozer - It'll plow through just about anything, and keep on doing it all day at maximum output.   And, yes, it has fans.  So does anything built to last that produces a LOT of power.  One of my ham buddies bought one and reached FT8 DXCC in just a couple of weeks with it, feeding a Hexbeam.  1500 watts.  On FT8.  With a Hexbeam.  Probably a small miracle the neighborhood did not catch fire.

So... there are MANY other (good) choices out there and many opinions.  These are just mine.

Have fun in your quest!

Brian - K6BRN
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K6AER
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Posts: 5689




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« Reply #6 on: April 12, 2019, 07:36:31 PM »

But could he reach DXCC on SSB in a few weeks? I doubt it.

For the price of a KPA1500 you could buy 2 ea. 2.3 KW tube amps. better to spend the saved money in a tower and antenna.
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K6BRN
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Posts: 1267




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« Reply #7 on: April 12, 2019, 08:59:03 PM »

Hi Michael (K6AER):

Quote
But could he reach DXCC on SSB in a few weeks? I doubt it.

Who cares?  Jerry is a die-hard CW tornado and contester.  The fact that he switched over to and adopted a brand-new DIGITAL/SOFTWARE-DRIVEN mode and made it sing in very short order to achieve DXCC (once again) is pretty remarkable.   I'M impressed.  Not many senior retirees/CW veterans can do that.   WAY TO GO!

And I think the KPA-1500 is his first solid-state amp, too.  Have to admire a ham who seizes new technology and wrings the best out of it:1,2,3.  Makes the rest of us look like... well... amateurs.

Quote
For the price of a KPA1500 you could buy 2 ea. 2.3 KW tube amps. better to spend the saved money in a tower and antenna.

I think Jerry already has a tower and antenna that he used to achive FT8 DXCC.  The Hexbeam antenna was a surprise - he can pretty much put up anything he wants.  He was probably just having fun. Which is the whole point.  And I'll bet he donated his old tube amp.  Money is not Jerry's problem.

He also switched over to a Flex-6600 as well.  As I said, remarkable adoption and mastering of new technology in very short order.  And he's a great mentor and asset to one of the clubs I'm in, too.  Nothing phoney about his expertise. He's "armed with a brain and knows how to use it".

(No...he's not paying me to say this - I'm genuinely impressed)

Brian - K6BRN

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KD0UYF
Member

Posts: 24




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« Reply #8 on: April 14, 2019, 06:20:26 PM »

With your criteria, the Acom 1200s is certainly worth a look.   Granted I've only owned mine a month, I couldn't be happier with it.  It is rated at 1000 watts continuous. I've ran 400-600 watts on FT8 for hours at a time without a single hiccup.  It does lack some of the features the KPA1500 and SPE Expert amps have, but if you dont need those, it is much easier on the wallet.
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N1UK
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Posts: 2219




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« Reply #9 on: April 15, 2019, 07:06:36 PM »

I am running the Acom A2100 on FT8 and it has performed well.  I did put a desk fan at the back to blow air over rear and side of the chassis where the tube is situated.  It helped to cool things a bit more when I was running 6m FT8 for an hour or so this summer.

I have noticed some tuning setting changes over time. I don't know if this is due to tube aging or other components suffering from my FT8 activities.


73 Mark  N1UK
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N5PG
Member

Posts: 1295




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« Reply #10 on: April 15, 2019, 09:44:12 PM »

There are some bargains to be had with old tube amplifiers, treated right they'll last you a very long time.
My issue with them is they're too large for the space available. There's a Drake L-4B and L-7 available locally right now.
« Last Edit: April 15, 2019, 09:50:00 PM by N5PG » Logged
K6BRN
Member

Posts: 1267




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« Reply #11 on: April 17, 2019, 08:53:22 AM »

Quote
There are some bargains to be had with old tube amplifiers

.... but most are missing 160M and 6M,  which the O.P. had desired.

Brian - K6BRN
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MM0IMC
Member

Posts: 230




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« Reply #12 on: May 14, 2019, 01:31:28 AM »

I use the Alpin 100 mkIII amplifier from Bulgaria. It's apparently got a beefier PSU in comparison to the Acom 1000 and has an external fan fitted as standard that you have to pay extra for on the Acom.

I use it every day on FT8 at the UK legal limit of 400W PEP. It covers top band to 6m with no problems...
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