Date: Fri, 02 Apr 2010 09:53:35 -0700
From: "Bill, W6WRT" <dezrat1242@yahoo.com>
Subject: Re: [Amps] LCR mteter.
On Fri, 2 Apr 2010 00:23:16 -0700, "Jim Thomson" <Jim.thom@telus.net>
wrote:
>## Not a chance Bill. Sure Myself, and everybody else does the
>same trick u do,,,, put a non inductive Resistor, between anode and chassis
>and the put the MFJ on the output, and activate the T/R relays.
>
>## Tune and load caps are then tweaked for flat swr on the MFJ. This
>procedure alone, doesn't help FINDING correct coil taps one bit !
>EG: I could easily have almost double the uh required for say 40m....
>and simply REDUCE the tune + load cap values.. till swr on mfj reads 1:1.
REPLY:
You say "not a chance Bill" and then you say you do exactly what I do.
What do you mean by "not a chance Bill"?
### I mean I wouldn't use the MFJ to measure the uh.. and
select taps based on uh readings from any mfj, when mfj used
to measure uh.
Second, when using the MFJ for this, the way I prefer is to preset the
tune cap for the value shown in the spreadsheets and then DO NOT TOUCH
it during the rest of the procedure. Adjust the load cap and change
the tap on the coil until you have the SWR 1:1. That way you end up
with the correct value of tune C and Q. Can't miss.
## sure, this method works good too. What do u use to measure the tune
cap ?? If the mfj is used to measure the tune cap, you will be out to
lunch.
If your AADE unit is used to measure the tune cap, all is well.
## I found that if I measured the taps with the b+K 875.. and tapped the
coil
using the spread sheet results..... everything came out just fine. When the
Tune cap
was checked [ after resonating the tune + load caps.. with mfj on the output]
after
the fact, it was dead on VS the spreadsheet. [ or extremely close]
Also, when pre-setting the tune cap, be sure to have the tube anode connected
so
it's capacitance is included too.
## agreed. The tube C will add another 33 pf on a 3CX-3000A7. That tube
C has already been factored in on the spread sheet. When the spreadsheet
wants
say 270pf for tune cap, it actually wants 303 pf..... but 33 pf comes
from the tube,
the C1 cap provides the balance...270pf.
If you are using a low frequency C-meter such as the AADE unit, disconnect the
plate
choke lest it throw the C measurement off.
## here I disagree. The effect of the plate choke is ALREADY factored in
..on the
spread sheet. My 200 uh plate choke will..'eat' 40 pf from my Tune cap on
160m.
That effect can be seen right away, when plate choke removed. With choke
removed,
the tune cap has to be REDUCED in value by exactly 40 pf. Change the value of
the
plate choke on the spread sheet, and you will see the effects on the value of
the
tune cap asap. Huge difference between 20uh, 200 uh.. and 99999 uh. [ 160m]
## to recap... the tube adds another 33 pf..... but the 200 uh plate choke
'eats'
40 pf. [160m] On the higher bands, the plate choke has a small effect.
## if the LCR meter. or what ever u use.. is more accurate measuring caps...
yes,
I would tweak the tune cap with it [ including tube and plate choke]. Then
use the same
lcr meter to get the coil tap in the ballpark. Then tweak the coil tap and
load cap to resonate.
I used to use a loaded Q of 12 [ = 10 using the old arrl/orr/eimac method..
which is just input
Q and not total Q] , I now use a loaded Q of 8-10. Eff improves, less
coil and band switch
heating, amp requires less adjustment, once tweaked at 14.200..... it's good
from 14.100 to
14.300 . Harmonic suppression might drop a bit, but the ant's are
monobanders, and swr on
the 2nd harmonic is sky high.... or is not inside a ham band. My 40 m yagi
does not resonate
on either 20m or 15m. I still use a LP filter.. with a 33 mhz cut off.
later........ Jim VE7RF
73, Bill W6WRT
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