[Amps] MRFE6VP61K25HR6

[Manfred Mornhinweg]

David, and all,

 > Isn't the MRFE6VP61K25HR6 device rated only 20% duty
 > cycle, pulsed, at 1KW?

It can do quite some more than that, but for true 1kW PEP SSB, with 
speech processing, the thermal issues are difficult to handle.

 >	How clean would such an amp be?

An amp using the board mentioned will likely not be very clean at all, 
as it doesn't seem to use any sort of negative feedback. But this can be 
corrected. When adding negative feedback, it will clean up a lot, and 
also it will require higher drive power, making it a better match for 
typical radios with 100 watt output stages. The ideal is to add so much 
negative feedback that it requires close to the full available drive 
power. That affords maximum linearity, and is a much better use of the 
available drive power, than burning it up in an attenuator!

 >	If one wants 1.2KW or better Output, and never have
 > to worry about losing a device, is the conservative path a
 > pair of these with a splitter-combiner?

Yes, but also adding some protective circuitry. To be very safe, I would 
include a current sensor in the supply line, a voltage sensor in the 
supply, a thermal sensor as close as possible to each transistor, and a 
power/SWR sensor. The outputs of all sensor can be joined, with proper 
individual tripping points and gains, to feed back to the ALC input of 
the driving radio, and to shut down the power supply of the amp if ALC 
action isn't sufficient to keep everything in the green range. This may 
sound complex, but is actually reasonably simple and very inexpensive to do.

 >	Power supplies are readily available and cheap but
 > when I was looking it seemed that the necessary switched
 > output filters are neither readily available nor much fun
 > to build.

Yes. The problem with these filters are the capacitors. They aren't easy 
to get, because some of them need to be rated for RF currents of at 
least 10A, the others for at least 5A. I'm also looking for good ones. 
The best I have seen so far are from England - a forum member hinted me 
about them. But even those are a bit on the tight side.

Homebrew copper clad mica capacitors are a good option, and perhaps 
using teflon instead of mica should be tried - but teflon is soft and 
has a lower dielectric constant. Its advantages are that it may be 
easier to get, and comes in better controlled thickness. Perhaps 
somebody has a good idea about other dielectric materials - I would love 
to hear it! It needs to be available in thin sheets, have good 
dielectric characteristics, it's desirable that it be tough, and it must 
survive soldering heat.

Manfred

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