This is a recurring debate, a bit off topic, but probably worth rehashing
from time to time. The science underlying our hobby is literally undeniable.
Further, there is a century of engineering history to guide future
developments. That said, as a practical matter, tinkering and
trial-and-error are almost always required when building an amplifier. That
doesn't mean the prior engineering and science is wrong, but rather that the
builder can't implement the theory exactly, because of unknown factors like
stray inductance and capacitance, variability in component specifications,
etc. For example, in my latest homebrew amplifier, a duo-band (80m-160m)
duo-band tetrode design, my time was divided into three roughly equal parts:
original design, fabrication, and debugging.
The tinkering part came in the debugging. I had motorboating in the screen
voltage regulator circuit, because of a poorly chosen time constant in a
feedback circuit; an overheated padding capacitor in the pi-L tank circuit,
because I hadn't verified the current rating of a doorknob capacitor; a
flashover in the HV circuit, because I hadn't used long enough standoffs to
isolate the HV fuse board adequately from the chassis; an inaccurate grid
meter reading because of excessive resistor variation in a voltage divider
network; RF hash on a dc-dc convertor because I'd skimped on the output
filtering; a poorly chosen ground point in the B-, which caused the
flashover current to damage a resistor when one of the Russian tubes arced
internally, etc., etc, etc.
My experience doesn't suggest that understanding the theory isn't important.
I'd still be tinkering away had I not cracked the books earlier in the
design phase. Furthermore, some of the circuitry (screen and control grid
regulators, QSK circuit) were new designs, which I never could have
undertaken without understanding the nuances of the circuits. So my "bottom
line" opinion is that sucessful homebrewing requires a combination of
theoretical underatanding, plus the ingenuity and intuition that comes only
from experience. The more complex the project, the more important the theory
becomes, but the debate shouldn't be theory vs. practice, because in my
opinion both are needed..
73,
Jim W8ZR
_______________________________________________
Amps mailing list
Amps@contesting.com
http://lists.contesting.com/mailman/listinfo/amps
|