Posted by
David F. Reed on
Jun 08, 2005; 7:05pm
URL: http://elecraft.85.s1.nabble.com/Dummy-Loads-and-SWR-tp379143p379148.html
Ron,
here you remind me of one of my favorite demonstrations; hopefully some
of the rest will enjoy my reminiscing.
>When dummy loads such as the Heath "Cantenna" first turned up in Hamshacks,
>they were a luxury item intended to replace the standard dummy load of the
>day: an incandescent light bulb. The light bulb had the added advantage of
>showing when the rig was tuned for maximum output by how brightly it glowed.
>
>
Years ago, I used to teach a class on high powered amplifiers, and the
importance of neutralization of the tank circuit was a topic frequently
covered.
I would take out an old knight kit T-60 (Yeah, I agree, certainly not
QRO, but effective for the demonstration) and hook it up to a 60 watt
incandescent bulb as a dummy load.
Then, with no crystal or VFO, I would key it down... the bulb would glow
as the parasitic oscillation came up, while we tuned the rig's plate and
load controls...
Then the challenge would be to neutralize it such that this could not
happen...
And back then, just a brief warning to turn the exciter off, and ground
the plate supply before working on it sufficed; we were a less litigious
society in those days I guess..
73 de W5SV, Dave
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