[R-390] Pulling crystal frequency in R390A

[Nelson Gietz]

Roger,
    Thanks for your information!
    I tacked a 5 pf cap across C524, and with that in, was able to move the 1 kHz peak to
coincide with the crystal frequency.  I’m reluctant to R&R the original C524 because the
coil leads may not take much more fiddling.  So, I’m good to go for the moment as far
as tuning Z501 is concerned, but still a bit dubious about L503 and/or C524.
    May track down a complete assembly for a spare if nothing else.
    Cheers,
    Nelson
    

From: Roger Ruszkowski 
Sent: Thursday, December 03, 2015 11:17 PM
To: ngietz at mymts.net ; r-390 at mailman.qth.net 
Subject: Re: [R-390] Pulling crystal frequency in R390A

Nelson,

You could have a problem in T205 if you can not get a good
band pass in the 1KHz bandwidth position.
The band does not "peak" you just try to put the center between the filter skirts.
Output in the 1 KHz band will be lower than in the 2 KHz band pass. 
The band width of the 1 KHz filter does not change with adjustment.
The circuit was designed and built close enough to specifications.
The adjustment just lets you move the band pass to center on the crystal where ever that may be.
At 2 KHz band width the filters are close enough to be over the 455 KHz crystal filter center.

6.2.17 in the Y2K manual give an alignment procedure for L503.

C524 in Z501 could be out of range.
A change of a few PF could let you bring the circuit back in alignment using L503 as it is.

Respectfully,

Roger Ruszkowski

-----Original Message-----
From: Nelson Gietz <ngietz at mymts.net>
To: r-390 <r-390 at mailman.qth.net>
Sent: Mon, Nov 30, 2015 9:40 pm
Subject: [R-390] Pulling crystal frequency in R390A

Going thru the alignment process on this R390A on the bench, I find that crystal Y501 for 
the narrowest bandwidths is about 80 Hz above the required 455 kHz. In the neutralizing 
procedure C520 adjusts well, but I can't get L503 to tune low enough to resonate the 1 kHz
bandwidth at the same frequency. There is no visible evidence of damage or tinkering in T205. 
Could the two problems be related? (The crystal resonant frequency is about 455.076 kHz
out of circuit.)
Also, has anyone heard of or tried "pulling" that crystal frequency to compensate? How
would that work in this circuit?
Nelson



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