[Amps] 2 kW amp project

[Peter Chadwick]

The article in QEX was not a simple multi band device, although I suppose it could eventually get to that. It uses a lot of cheap FETs, and goes up to 7 MHz. Going up to 28MHz with cheap FETs may not be on. The output transformer is fearsome, with 1/2 inch copper tubes silver soldered to 1/8 inch thick copper heatspreaders. Copper is vile stuff to work, too, when it comes to drilling and tapping. Incidentally, it behoves one to be careful when working with sheet copper, since any small cuts that you get from it frequently tend to get infected and take a long time to heal - although not as long as RF burns!
The problem with Class E is that it isn't linear, although it modulates well for AM. This suggests that for SSB, either a Cartesian or Polar loop approach is required, which adds considerably to the complexity - possibly a Callum modulator could be used, but that's fairly critical on set up, too. Personally, I need some convincing that at the end of the day, for homebrew ham use, the big SS amp really wins out. From the viewpoint of interesting technical experimentation, there is a lot of fun to had from it, though. One major factor for a linear amplifier is still the heatsinking. Teaching grandmama to suck eggs here, but a larger allowable temperature rise means that the cooling is less critical.
Accepting the switching regulator (and high voltage SMPS are available), I doubt the tube amp ends up much different in size and weight. There is the minor problem of making sure the SMPS is electrically quiet enough, of course. OK, you can switch it off on receive, but if it requires a surge limitation on input current, QSK would be a problem.
The tube amp with the 75lb HV transformer isn't likely to get easily knocked off the table, though!

73

Peter G3RZP







========================================
Message Received: Nov 21 2005, 12:48 AM
From: "Bill Turner" 
To: "wc6w at juno.com" , Amps at contesting.com
Cc: 
Subject: Re: [Amps] 2 kW amp project

At 09:54 AM 11/20/2005, wc6w at juno.com wrote:

>Hi Bill,
> Item #1 is easy. Get a surplus 48V switching power supply from 
> the telecom world.
>
> My best suggestion for #2 is a dual pi-net. 50 ohms to 500-1000 
> ohms back to 25-100 ohms. This provides both matching & harmonic 
> suppression. Two switched coils, 3 (small) vac. variables, plus 
> some ceramic padders for 80 & 160. Physically about 6" x 7" x 12" 
> including motor drives for the caps & 10 position bandswitch.
>
>73 & Good morning,
> Marv WC6W

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Sounds good. I almost wish I hadn't started the 8877 project but it's 
too far along to stop now. :-)

Where does one find the surplus telecom supplies? Can you suggest a 
manufacturer of new ones?

73, Bill W6WRT

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