Rich said:
Rich said:
"If your DAF amp measures minus 22db total IMD, YOU foolishly selected
the wrong tube."
Rich, you have continually cited a -22 db 3rd order imd for the "DAF"
design. However, when pinned down the last go around, it became obvious
those numbers are false. Assuming your measurment numbers are correct, it
was not on the G2DAF amplifier. It was measured on a poor copy. In fact,
one of your measurements was made upon Norm's version, which hung a 2 ufd
capacitor across the screen to ground. And, it was a cathode driven
circuit, to boot. It had nothing in common with the original circuit. You
have used your measurements of the wrong amplifier as a basis for rejecting
all constructive analysis or criticism of the original circuit.
Your comments are unscientific and unsubstantiated. You have used
this -22db measurement as a smoke screen. And, then, you seem to say that
every test made on the G2DAF circuit is flawed as you are the only one who
can perform that unannounced test. Yet, you are willing to condemn the same
amplifier based upon your measurements of the wrong amplifier.
Please, when you decide to do your test, make sure it is the G2DAF amplifier
you are testing. Somehow, I think if it passes, you will question that
another amplifier was substituted. But, if it fails - as Norm's did - you
will be convinced it was the true design.
One of my close friends is an engineer. In the early 60's, he worked at
Tektronix. Other engineers were working to raise the frequency response of
oscilloscopes to 50 mhz. While they were doing that, he was off in a corner
experimenting with designs that did not work. The first thing he did was
design a power supply using a 4CX250F in a modified socket. Then, he began
designing a front end for the new scope using hardline coax. His
contemporaries thought he was nuts. None of his design used generally
accepted "good engineering practices". He would have been fired had it not
been for the fact that he held many patents and was otherwise considered
brilliant.
Soon, he demonstrated his nutty design. While other scopes had a bandwidth
of 50 mhz, Cliff's model 519 prototype could go over 1 ghz. Although it was
special use, it was in production and served a valuable function in
scientific discovery for over 20 years.
My point is that good engineering practice is a matter of opinion.
Colin K7FM
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