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

[Kevin Schuchmann]

Jacques,
   I went back was was much more precise in my voltage readings, skipped the approximately 6 volts and went for 6 volts exact.
That gave me two nulls with a center position, and if referencing the angle compared to the center mark then they are both way less than 45.
The tuning coil was also a bit off so maybe adjusting that also helped, I went through it all several times.
I'm happy with the results at this point and everything seems to be working well.

As always thanks for the help
Kevin




On Tuesday, January 7th, 2025 at 1:11 PM, Jacques Fortin <jacques.f at videotron.ca> wrote:

> 
> 
> 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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