Several readers asked that I provide an update to
my 3-1000Z pi-network input tuned circuit chart after
I had completed the replacement of the National XR-50
slug tuned coil with a powdered iron core in my 160M
monoband amplifier. It took less than an hour to complete
the replacement this evening. The complete table of 160-10
meter pi-network component values follows this text.
As a reminder, count the "turns" in any toroidal inductor
by counting the number of times that the wire passes thru
the center of the core. Yes, this results in a turns count
exactly one turn greater than you might count intuitively.
Input tuned circuit configuration notes:
A 0.02 uF mica blocking capacitor is connected directly in
series between the exciter and the input of the pi-network.
C(in) is the pi-network capacitor on the exciter side of
the pi-network. It is grounded to exactly the same ground lug
C(out) is the pi-network capacitor on the 3-1000Z side
of the pi-network. This capacitor is connected directly from
the filament pin to a ground lug on the chassis immediately
adjacent to the 3-1000Z filament pin.
An additional 0.02 uF mica capacitor is connected between
the filament pins to keep them at the same RF potential.
Final input tuned circuit pi-network values:
Band C (in) Powdered Iron Toroid C (out)
160 3700 25 turns #22 on a T68-2 (red) 3000
80 1820 17 turns #22 on a T68-2 (red) 1500
40 910 14 turns #22 on a T50-6 (yellow) 750
20 470 10 turns #18 on a T50-10 (black) 360
15 300 8 turns #18 on a T50-10 (black) 240
10 240 6 turns #18 on a T50-10 (black) 180
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