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Author Topic: Class C Power Amplifier for CW  (Read 515 times)

N0PP

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Class C Power Amplifier for CW
« on: January 27, 2022, 07:26:36 AM »

Looking at the QRP Labs 50 W power amplifier on http://qrp-labs.com/50wpa , how easy (or not) is it to scale that design up to higher power levels, say 500 W? Can I get away with "just beefing up" the transistors, toroids, power supply, etc., or am I entering a whole new world and need a completely different design?
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W1VT

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Re: Class C Power Amplifier for CW
« Reply #1 on: January 27, 2022, 07:29:53 AM »

It is easier if you are willing to increase the voltages substantially so that you don't have to change the required impedance ratios.

From the web page
"Up to 50W power output on 40m with 20V supply, falling to around 25W at 13.8V supply"

Trying to stick with 13.8V makes things a lot harder.
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N7EKU

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Re: Class C Power Amplifier for CW
« Reply #2 on: January 27, 2022, 07:42:01 AM »

Looking at the QRP Labs 50 W power amplifier on http://qrp-labs.com/50wpa , how easy (or not) is it to scale that design up to higher power levels, say 500 W? Can I get away with "just beefing up" the transistors, toroids, power supply, etc., or am I entering a whole new world and need a completely different design?

It would for sure be the last part you said!
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Mark -- N7EKU/VE3

N0PP

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Re: Class C Power Amplifier for CW
« Reply #3 on: January 27, 2022, 07:57:54 AM »

Thank you for your insights W1VT and N7EKU!

Are there any good resources out there that will help me getting started with higher power solid state amplifiers? Any good books, online resources?
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W1VT

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Re: Class C Power Amplifier for CW
« Reply #4 on: January 27, 2022, 08:07:14 AM »

https://www.eham.net/article/42414
Little Boy -- A Water Cooled LDMOSFET Amplifier
Created by W6KAN on 2019-03-22
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K7MEM

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Re: Class C Power Amplifier for CW
« Reply #5 on: January 27, 2022, 12:30:51 PM »

Are there any good resources out there that will help me getting started with higher power solid state amplifiers? Any good books, online resources?

Back in the day, when semiconductor manufacturers generated paper manuals, Motorola created a group of Application Notes and Engineering Bulletins on Linear Amplifiers. Here are a couple of them.

EB-63

EB-27A

AN-762

There are a lot of other ones archived on the internet. I have the original manuals. Many of these designs were scooped up by the CB crowd to create high power amplifiers. They are actually good designs. I have one that puts out 130 watts with 5 watts input and covers 3-30 MHz. Although, I did have to add some input/output filtering and change the keying.

While these aren't Class-C they should give you an idea of what's involved.
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Martin - K7MEM
http://www.k7mem.com

KH2BR

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Re: Class C Power Amplifier for CW
« Reply #6 on: January 31, 2022, 07:52:32 AM »

All of your problems are solved here. !!!
https://rfpowertools.ecwid.com/
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AC2EU

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Re: Class C Power Amplifier for CW
« Reply #7 on: January 31, 2022, 08:23:19 AM »

All of your problems are solved here. !!!
https://rfpowertools.ecwid.com/

They say the board is based on AN1819 application notes. I could not find that document!

AC2EU

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Re: Class C Power Amplifier for CW
« Reply #9 on: January 31, 2022, 10:27:30 AM »

https://www.microsemi.com/document-portal/doc_view/132525-a-700w-broadband-amplifier-using-vrf2944

OK thanks.

However this too, is based on a 50V supply . The OP wanted it to run on 12.6V
Zo to match on a 12.6V 500W amp would need to be a third of an ohm. 

WA3SKN

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Re: Class C Power Amplifier for CW
« Reply #10 on: February 05, 2022, 03:22:22 PM »

NO!
You will have to replace everything including the heat sink to get to the 500 watt output level.  You might as well design for 500 watts from the start.  It will probably not be a $30 kit either.  And don't plan on using a 13.8 volt power supply at 500 watts.
73s.

-Mike.
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