[R-390] noob and Z501 in a non-A 390

[Jacques Fortin]

Kevin, there is TWO capacitor positions for which the output became minimum
for both sides of the peak.
Remember how those Erie trimmers are made ? 
There is two positions of the rotor that gives the same capacitance value.
One of these "pair" of settings will be less than 45 degrees apart, the
other pair, well... maybe not.
>From the TM11-5820-357-35, chapter 76: 

To avoid possible incorrect readings, caused by tuning thru the positions of
minimum or maximum capacitance, the two capacitor settings for minimum
output must be less than 45deg. apart.

My interpretation is that if the capacitor position is adjusted in the
middle of a "pair" of positions more than 45 deg. apart, this is not the
right setting.

>From my notes, I had no problems when I have done this alignment on mine.

73, Jacques, VE2JFE in Montreal

-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la
part de Kevin Schuchmann via R-390
Envoyé : 7 janvier 2025 14:52
À : Collins R-390 HF Receiver List <r-390 at mailman.qth.net>
Objet : [R-390] noob and Z501 in a non-A 390

Hi All,

Got my replacement audio transformer and thought while the radio is out of
the cabinet lets do an alignment.

I'm stuck on adjusting Z501 as my nulls are much more than 45 degrees apart.

Following the 31R1-2URR-412 manual I found my peak at 455.10 KHz and after
peaking the IF for 6 volts on the diode I require a -82.0dBm signal.
So page 93 step k says to increase the signal a 1000 times and if my math is
correct that should be -52dBm and then tune off until I am at 6 volts again
which turns out to be 455.91 KHz.
Then adjust the capacitor until i get minimum signal and I get 1.1V and I
mark the location of the capacitor.
Then step M says to tune to the opposite side of peak with the increased
signal gen output and I end up at 453.79KHz for 6 volts.
I then tune the cap again for minimum which is 340mv and now put the
capacitor in the middle of the two spots.

It warns that the two minimum spots must be less than 45 degrees apart, mine
are very close to 90 degrees apart.

What am I doing wrong here??????

Thanks
Kevin
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