[Amps] How light can you make a 500W amplifier?

[Peter Frenning, OZ1PIF]

Well, I've built a 500W 50MHz amplifier, which weighs in at a little over
8KGs all included. It's MOSFET (16 x low-cost IRF510s!), and has a switching
PS (bought very cheaply as surplus).

IMD is better than 30dB (limited by signal amplifier used for measurement)
and has a better than -65dB elliptical low-pass filter. The whole thing
measures 40x30x18cm, and could be made lighter. The heavy components are the
heat-sink (big heavy one from the junk box), and the enclosure (2mm steel
plate, also from the scrap heap)

So it aint HF/multiband, but so what?, it could easily be converted to work
on any single HF band, and (not so easily (there are som gain issues)) to a
switched multibander.

I got the basic circuit design from OZ3SW, who is still working on his
band-switched HF multibander, and my 50MHz adaptation of his basic circuit
has been successfully reproduced by others. I am in the process of writing
it up for publication.

Some data:
    gain = ~14dB @ 40V
    Pout (key down) 500W/19.5A or ~ 800W DC input

It's been up and running since before christmas last year, and has worked
flawlessly ever since (except for a case of fireworks, for which I was
responsible - I forgot to reduce the drive to the required 20W, and actually
ran it for 5 QSOs before it blew, (no comments about distortion or
splatter!) I simply replaced all 16 IRF510s (grand total < $10) and was
ready again (I have now included an attenuator to prevent it from happening
again)

Vy 73 de OZ1PIF, Peter

**********  OZ1PIF **************
email: oz1pif(no-spam-filler)@get2net.dk
http://hjem.get2net.dk/oz1pif
Ph. +45 4619 3239
Snailmail:
Peter Frenning
Ternevej 23
DK-4130 Viby Sj.
Denmark
***********************************
----- Original Message -----
From: "Alan Ibbetson" <g3xaq@hotmail.com>
To: <amps@contesting.com>
Sent: Monday, October 14, 2002 9:34 PM
Subject: [Amps] How light can you make a 500W amplifier?


> While exchanging tall tales at the bar at the RSGB HF Convention over the
> weekend the discussion came round to the need for an amplifier
specifically
> optimised for solo DXpedition use. The holy grail is 500W output on the HF
> bands at an all-up weight of around 10Kg. The well known semi-pro MOSFET
> amplifier on the market has a dreadful reputation for IMD and is pretty
much
> unobtainable anyway. Thermionics seem more appropriate, but their power
> supplies are heavy.
>
> What is the list’s collected wisdom? Solid state? Valves, perhaps with
SMPS?
> Theorising is OK (after all, it was a bar room discussion), but what would
> really get my attention is a URL to an actual example of a 500W/10Kg
> product.
>
> 73
>
> Alan G3XAQ
>
>
>
>
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