>> From: Rich Measures <measures@vc.net>
>> >Rich comments;-
>> >> The statement that I did
>> >>not buy is that drawing grid current (Class AB2) decreases IMD. I use
>> >a
>> >>Class AB1 amplifier, and I know that such a statement is unsliced
>> >>bologna. ..... AB2=doo-doo.
>
>Peter said....
>
>> >Then my spectrum analyser is a liar. ...........
>
>Rich said...
>.
>> Another scenario seems a bit more likely.
>> Rich---
>
>Rich,
>
>Peter is correct.
However, I could not help but noticing that Peter's statement did NOT
receive the "exactly correct", "precisely correct", or the even-higher
"EXACTLY correct" rating. This leads me to believe that Peter's
statement could very well be slightly flawed.
...snip...
>Class AB1 does not always guarantee better IMD performance. Even
>though your "on the air tests" may have indicated YOUR PA was cleaner
>when AB1, you should remember you insist on using a "crummy bias
>system".
Eimac recommends using a 100k ohm or less Rout bias supply. My bias
supply V-divider utilizes a 5000 ohm wirewound potentiometer, so the Rout
is probably on the order of several thousand ohms. If this is "crummy",
Eimac's recommendation is "crummy".
>
>With the stiffer bias system Ian suggested, your "big amp" might
>not have been such a splatter box at high drive levels.
>
The drive level did not change during the test. Increased splatter was
observed when the bias V was reduced so that grid current began to flow.
Rich---
R. L. Measures, 805-386-3734, AG6K
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