For anyone wondering what the suggestion re revised bias was about, schematic given above. I? have used a known good schematic? and marked it up.? so there are no doubts it has been proven , at least with? and RD16HH? 20 W amp.
Changes required.? R5 and R6 become 100 - 120R , to match the? 1:4 transformation provided by the trifilar transformer.? Mosfets? of course? become IRF 510.? The return path for gate current in? Q2 would? be to GND and across the gnd plane, back through R6 and to the opposite? secondary leg of the trifilar transformer .??
If the? IRF 510 Mosfets? are represented by about? 20 - 200 j as a? gate impedance at frequency? then the 100R? ?Resistor plus gate pair? as a parallel unit represent about? ?80 < -40 or? 61.3 -51.4 j and? as a series set Q2//R and Q3//R? then 160 <40 ohms which is a lot better SWR match and much lower reactance? than will be given by the mosfet gates alone in the? std? CW 50 W amp cct.? The? original bias potentiometer still applies of course.?
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Correction-?
From previous post - for the? calc of SWR corresponding to an RD16HH with no loading resistor .
ZL - Zo /? ZL+Zo?
or? ((20- 50)Re? ?- 90j) /( 70 MINUS? 90j)?
which? simplifies to about? 0.832? <-56? ?( angle? - 56 deg)
The bold shows the change made.? The mag? and angle were calculated correctly.? The error was transcribing from paper
to the? typed version??
?
Timothy Fidler