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Author Topic: Building an HF amplifier  (Read 551 times)

Matt285

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Building an HF amplifier
« on: April 16, 2021, 1510 UTC »
This may not be an exact fit for this category, but since it involves ham radio, I'm gonna go for it. So I see on Ebay and various sites that there are HF amplifier kits 200 watts and up. The kits are pretty cheap, although I realize they don't include heat sinks, Mosfets etc. How much money would it cost to build an HF amplifier 200 watts and up? And also how much extra parts and skill are required? It doesn't seem like it's a common thing when I talk to other hams. I'm thinking there must be a reason why hundreds of thousands of people are willing to pay $1000.00 and up for amplifiers.

Offline RobRich

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Re: Building an HF amplifier
« Reply #1 on: April 16, 2021, 1911 UTC »
The kits are tempting. Just remember you need more than the MOSFETs, heatsinks, relays. For example, you are going to need to buy or build a lowpass filter board capable of covering each desired operating band. You might want metering. That is another circuit. You probably want some type of protection, say for severe SWR mismatch. That is yet another circuit. Toss in a power supply, too.

I like the idea of building. It teaches electronics skills. Though if perhaps more interested in operating, compare what you are going to spend building, not mention the potential hassle, against buying. Check QRZ and similar for used deals. A common example is an used working AL-811(/H) with good tubes, and especially if swapped to 572B tubes, is a popular affordable HF amp for a few hundred watts. Drive it reasonably, not for absolute PEP output, and it probably will last for years of service.
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Matt285

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Re: Building an HF amplifier
« Reply #2 on: April 16, 2021, 1917 UTC »
Thanks for the reply. I wish 20M amps were as common as 10M amps. You could probably modify a bit and make one work.

Offline Stretchyman

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Re: Building an HF amplifier
« Reply #3 on: April 17, 2021, 0753 UTC »
I'd stick to the BLF188XR as you can get an easy 800W from 5W driving. The 200W kits with IRF devices are fairly old designs and not the best.

Depends what you're looking for?

Band switching is the most problematic part!

Str.
'It's better to give than receive' so why RX when you can TX!

         15W and100W models available.

                   Buy one from me, NOW!


                                              ;)

Offline redhat

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Re: Building an HF amplifier
« Reply #4 on: April 17, 2021, 1815 UTC »
I'd stick to the BLF188XR as you can get an easy 800W from 5W driving. The 200W kits with IRF devices are fairly old designs and not the best.

Depends what you're looking for?

Band switching is the most problematic part!

Str.

BLF188/184 are now EOL pending replacement devices which have yet to be released.  I found that out repairing a 5KW FM recently.

Also keep in mind unless you are willing to solder the devices to a heatsink, the newer gemini devices are totally unsuitable for full limit linear service.  Lots of power in a small space, a thermal management nightmare.

+-RH
« Last Edit: April 17, 2021, 1817 UTC by redhat »
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Offline Stretchyman

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Re: Building an HF amplifier
« Reply #5 on: April 17, 2021, 1909 UTC »
Heatspreader, MASSIVE fan etc.

I'm not a fan of linears as they're so inefficient.

For A.M. class E is so simple and you can generate bucket loads of power with cheap devices and simple circuitry and efficiency is 90+%

SSB has to be linear obvs.

I'm sticking with A.M!

Str.
'It's better to give than receive' so why RX when you can TX!

         15W and100W models available.

                   Buy one from me, NOW!


                                              ;)

Offline redhat

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Re: Building an HF amplifier
« Reply #6 on: April 17, 2021, 2022 UTC »
FWIW, you could buy one of the many kits off ebay such as... https://www.ebay.com/itm/MRF300-LDMOS-600W-HF-LINEAR-AMPLIFIER-1-8-54MHz-BOARD/233929540038?hash=item36774981c6:g:dYMAAOSwwkhgQO9Z

Just supply fets, heatsink, and off you go.  600W fairly simple as all the hard work is done for you.

BTW you can do high level SSB using the kahn method.  Continental and others have been doing it for over 30 years...without DSP, and at hundreds of KW.

+-RH
Somewhere under the stars...
WinRadio Excalibur, Airspy HF+, Kenwood KDC-U356 for mobile listening.
Please send QSL's and reception reports to xfmshortwave [at] gmail [d0t] com