> Rather than do all this guessing and wondering and trying to re-invent
> the wheel, why don't you pose your questions and theories to the folks
> at CDE or HEC or ATC: they're the ones that stamp the current ratings
> on their parts, not us. Asking us what an "8.5 amp rating means to us"
> is pointless. It means 8.5 amps.
The method of determining ratings are defined in the technical
literature. For example, the "current rating" specified by HEC and
Jennings is for a certain starting ambient temperature, a certain
heatsink configuration (as I recall they selected operation with no
heatsink like a large chassis bolted to the leads and no cooling
airflow), a certain duty cycle, a certain defined temperature rise
that they picked that was well under the maximum temperature rating
(the user can vary or adjust with his particular application as long
as he stays below the maximum allowed maximum temperature), and a
certain frequency.
With capacitors it is generally the ambient temperature, duty cycle,
frequency, and allowable temperature rise.
What screws it all up with the doorknobs is they change value at a
rate higher than the temperature coefficient stamped on the part, and
that is subject to change depending on the processing. That's why for
many years Ameritron used three 500pF DK in parallel on 160, and had
no problems. Later, with no change in the PA design or construction,
the components changed and a drift problem cropped up that according
to data should never have occurred.
Very few components listed as "xx amperes" have that value etched in
stone. Even something as simple as fuses generally have several
factors to consider.73, Tom W8JI
W8JI@contesting.com
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