>
>Ohh, this parasitic nonsense again?
>
>> I'm sure using a sledge-hammer to drive paneling nails works, but
>> honestly, it's better to do the job right to begin with.
>>
>> If a parasitic can be determined and suppressed, without the need for
>> brute force automatic shutdown of a circuit, then that is IMHO, the
>> correct choice (at least until someone shows me that tree 8877's grow
>> on).
>
>8877's have had poor service history while they were at Salt Lake.
>While there were periods of time in the 80's when you couldn't get
>a tube that lasted over a few hours, there were periods when they
>were fine.
>
>They just aren't as long lasting a tube as a thoriated tungsten tube,
>or a tube with wider internal spacing between grid and cathode.
>
>Tubes in the 80's were so bad we ran 8877's in a tester (like we do
>3-500ZG's now) that cycled the filament off and on, and had a
>latching SCR between the reversed biased grid and the cathode,
>watching for shorts. We'd come in after cycling a batch of tubes
>overnight, and six or more fault lights would be glowing out of every
>eight tubes.
>
>8877's failed in voltage regulators, in MRI gear, in BC stations, as
>well as in Ham gear like AL1500's. They failed in nichrome loaded
>amplifiers, and they failed in tube testers that don't even apply HV
>to the tube.
>
>As tough as it might be to swallow for some people, tubes are the
>weakest and most unreliable link in ANY gear. And if you mistune
>a PA, or run it without a load or if the load faults just for a
>millisecond, something will often arc. We may like to blame
>everything on the parasitic fairy, but there are multiple causes of
>failures.
>
>The parasitic nonsense about damaging switches
// see such "nonsence" at:
http://www.vcnet.com/measures/bandsw.html
>and tubes has
>been gone over a thousand times, and those that "believe" are
>welcome to believe. It's Christmas, and I'm sure some people really
>believe in Santa.
// The Red Herring
>After ten or fifteen years of what amounts to only
>one person fueling the fires, there is little reason to point out the
>same clear and proven technical points over and over again.
>73, Tom W8JI
>W8JI@contesting.com
>
// So why did you stonewall me six times during the Grate Parasitics
Debate when I asked you: is there a VHF parasitic suppressior in the
AL-1500? (a disloyal AL-1500 owner eventually informed me that there
isn't any).
- R. L. Measures, 805.386.3734,AG6K, www.vcnet.com/measures.
end
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