Hi Jim,
If I was the Personnel Director at some highfaluting industrial complex,
looking to hire-on engineers, I would make special note of the applicants'
hands when shaking them...
Any absence of calluses, cuts, bruises, scabs, scars, blisters, etc. etc. etc.
would immediately tell me that THIS particular wannabe engineer is strictly a
BOOK-learned specimen, and NOT a "tinkerer, experimenter" that maybe works on
his / her car in their spare time, etc.
Call it the School of Hard Knocks---whatever. Practical experience goes
hand-in-hand with theory, & too much of one, without the other, is NFG, IMHO...
Eddy
On 2015-01-12, at 11:11 AM, Jim Garland wrote:
> 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
>
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