: [Amps] Tuned input design / measurement questions
16/04/2013 16:34
May I ask a question re my construction of a tuned input circuit? I am
converting a Henry 2000D RF Generator on 27.12 MHz to (initially) a
single band (20 meter) linear amp. I am trying to build the tuned
input circuit, after checking it works on 27 MHz. The 3CX3000A7 valve
has a cathode input impedance of about 48 Ohms. It has a stock Henry
Pi input tuned circuit comprising a slug tuned coil on a half inch
diameter former (about 4 turns 20 gauge wire), and two sets of
paralleled dipped silver mica caps each side of the coil, to ground. I
have acquired a new henry former and have wound it to give .475 uH on
my AIM 4170 analyser. I have a pair of air variable caps of about 350
PF max each. I have built it as per the photos at:
http://www.chriswilson.tv/pi/input_pi.zip
The idea of this Pi circuit came from my reading and is to
is to add Q and give a flywheel effect, ideally needed in Class AB GG
linear inputs.
http://www.eham.net/ehamforum/smf/index.php?topic=12665.0
See last post by W8JI Tom Raunch.
You all know this of course, don't get me wrong, just showing my source!
Yeah while his explanation appears OK its this line that gets many laughing:
---------------------
"That may or not be an issue with your SB-200. I can not recall the coponent
values of the SB-200, it was designed long before I designed products for
Heath."
----------------------
There werent enough on the Internet in early 2001 to question his resume
accuracy...........
Carl
KM1H
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