> It prompted me to re-read my technical description of our PLA-800 and
> discover the error that was being discussed.
Actually 4CX250's are among the poorest tubes for IMD. Was you
amp ever type accepted? What is the TA number? I did an FCC
database search, and couldn't find it.
You know of course any amplifier of more than one unit per year for
use below 144 MHz must be type accepted, can not have gain on
25-35 MHz, and must not include RF T/R switching. It also has
gain limits, requiring at least 50 watts of drive whether it is 10 watts
output or 1500 watts in design.
> The issue of screen current regulation was a typo mistake and we apologize
> for any misrepresentation. The web page has been corrected to say,
> "screen voltage regulation and plate overload protection". On the issue
> of IMD, if tetrodes can exhibit more IMD, why did Collins, Westinghouse
> and Gates use TETRODES?
1.) Because they needed the high gain
2.) Because they used tetrodes designed for the service they were
used in
> I am pleased with the use of this forum however, as it can point out
> mistakes or mis interpretations of product manufactures and can be viewed
> as a useful communications medium.
All advertising and marketing claims about "clean tetrodes" aside,
if you look at tetrode amps for amateur service they typically have
much poorer IMD performance than triodes.
When you tested and submitted your TA papers for the amp you
sell, did you also do a IMD test even though the IMD test is not
required? I wonder how many manufacturers check to see how
clean their PA's are before marketing them, since everyone (even
those selling parts kits to Hams) is required to file and get TA.
73, Tom W8JI
W8JI@contesting.com
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