Dick,
I have to believe that M2 knows what they are doing with these Amps. They
offer a 12 month limited warranty on them.
I really hope so! I know nobody who owns one of those amps and uses it
intensively, so I frankly have no idea whether or not they last. But if
they do last, I would like to understand how and why! It is totally
possible and even likely that the difference between my highly
simplified math, and a really accurate calculation, would explain it,
and show those amps to run the FETs within specs. But I have certainly
seen many devices, specially power supplies and linear amps, built buy
hams, that suffer failures because of totally wrong thermal design.
That's why I wanted to bring this issue to the attention to those
wanting to milk any high power transistors to their maximum ratings.
And then, it is well known that manufacturers are not always right in
everything they do, even when they give warranty! Just think about all
those many known cases of typical failures, that end up affecting most
or all radios of some specific model. Some examples: The Kenwood TS-440
with its glue that degrades and makes the VCOs fail; the TM-241 with its
display going crazy because of a tiny interboard connector that develops
excessive contact resistance; the old Yaesy FT-207 in which the
10.245Mhz crystal cracked from excessive drive; The FT-ONE, which had a
crystal that shifted several tens of kilohertz over twenty years; The
Icom IC-746 series with its several thermal problems, such as with the
pre-driver transistor, the wideband amplifier IC, and the transistor
that regulates the display brighness - all these coming from incorrect
thermal handling of SMDs. Do you want more? The rotting DDS chips in the
TS-450 and TS-850, the many problems of connectors directly soldered to
circuit boards, in many radios of most brands, so that those solder
joints break, assorted trouble with breaking solder joints on PCBs when
too heavy parts are supported solely from the solder joints, and so on.
Even the most professional designers at the best known companies are
only humans, and do goof at times! So do the providers of components and
materials.
The single most intriguing issue of misdesign, that I would like to
fully understand, is that matter of incorrectly understood and applied
transformers in push pull amplifiers. I have explained this in full on
this page of my site:
http://ludens.cl/Electron/mosfetamps/amps.html
I mean the section entitled "Output architectures of conventional class
AB push-pull amplifiers".
This is a typical case of "it's not possible that all manufacturers are
wrong and just XQ6FOD is right". It does feel weird to me to stand up
against all those that make their money building and selling
transceivers containing that bug! Nevertheless I simply don't see how it
could be right their way. I first discovered this problem in homebuilt
equipment 30 years ago, when I copied circuits from ARRL literature, and
have later confirmed in in actual factory made radios from the big
brands, and also by simulation. Recently a German ham contacted me,
reporting that he built two test amplifiers (100W, 13.8V), which were
identical except for the issue I describe, and that he measured a modest
but noticeable (3dB) improvement in gain, a significant improvement in
efficiency, and a big improvement in IMD performance, when using the
layout I consider correct, compared to the one most present-day HF
radios use.
Go figure.
I would really love to see either a statement by some RF guru, declaring
that I'm right and they are wrong, and hopefully giving an explanation
of how this mistake became so widespread, or else someone (whether he is
a guru or not) who can explain why the method used by manufacturers in
some radios and also propagated by Granberg et al in some papers and
copied by the ARRL (center-tapping a single-turn winding that has
independent magnetic paths for each half winding) is correct!
Manfred
========================
Visit my hobby homepage!
http://ludens.cl
========================
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|