Gents,
I have to say that Colin and Marv seems to be the most open minded people
on this reflector at the moment. At least they try to understand what is
going on and even suggest some improvements.
Two tone tests have been used as a standard to evaluate amplifiers since
donkeys years. Now this test is not telling the truth say's the gurus.. ok,
I accept the doubts on given grounds.
But maybe we should start testing other amps than DAF's without using the
two tone test. A poorly regulated screen power supply in a grid driven amp
should maintain a pretty stable voltage with a two tone constant modulation
not giving away that the amp would sound bad when modulated by speech. True
or not .. ?
Lars, SM3BDZ has published a number of plots on his website showing the
performance of his DAF amp under different conditions. To rule out "the
error" of a two tone test on a DAF he has plots of speech instead. Plots
were made using first class commercial test gear. Check them out and you
will see that the thing works.
But I do most certainly agree with Marv and Colin that the DAF circuit is
not going to work with every tube on the shelf, the 4CX250's for instance
are a NO GO for sure. Just like some tubes don't work in GG.
One fellow on this reflector who certainly doubts the DAF circuit found me
on the band by chance one time and listened carefully to my signal He
reported on the reflector that it was clean and the IMD was indeed ok. But
we must of course rule him out as he knew my call and could possibly be "a
kind fellow".
Tom, you are correct about people reporting "excellent quality" to signals
that sound terrible just because they lack knowledge or maybe sponsor
"friendship". Therefore it is essential that bench tests are carried out
and when testing on the air you must know that the fellow(s) are checking
your signal out have the knowledge and the integrity needed. Very true.
Rich will not check a signal out if he knows that the guy transmitting
knows he is listening... follow me.. ? So, I can never get him to check my
signal out with his proffessional methods/ears as we never meet on the
bands and we can't make a sked because then I migh be cheating in his
opinion.
So I continue to populate the bands with my DAF amp and get clobbered in
the contests from people moving closer and closer in frequency because they
are able to do so without suffering.
I hear so many poor IMD signals on the band where I know the guys are using
state of the art GG or grid driven amps that I am convinced that the -35db
two tone IMD they "should" produce is just BS. Then again, there are many
amps of the same kind that sound marvellous. What's the difference ? Let's
find out !!!!!!! Let's start measuring speech modulated rf instead of
steady two tone rf on ALL amps!
I do not tell people to build a DAF amp, I just tell them how mine works
and they can make their mind up themselves.
Ciao,
Mr Peter SM2CEW
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