[R-390] IF Alignment in the R390/URR

[Barry]

Larry, Jim,

Thank you for the explanation regarding the crystal filter.  I didn't realize that was the dominating part of the circuitry for that.  It makes sense to me now.

Thanks again,
Barry - N4BUQ

----- Original Message -----
> From: "Barry Scott" <72volkswagon at gmail.com>
> To: "R-390 Mailing List" <r-390 at mailman.qth.net>
> Sent: Sunday, October 20, 2024 7:08:48 PM
> Subject: [R-390] IF Alignment in the R390/URR

> The IF alignment instructions for the R390/URR (and, and I recall, the
> R390A/URR as well ) begin by adjusting the signal generator to the
> frequency that provides the highest voltage on the DIODE LOAD.
> Apparently, this is not always 455.000kc but I'm not sure I follow why
> it isn't.
> 
> When I read this, I made a possibly false assumption that having a
> signal generator with a precision readout or an accurate counter
> wasn't usually available and adjusting for the "best" frequency was
> the best approach.  When I aligned mine, I chose to use 455.000kc but
> now I'm wondering if that was a mistake.  The primary reason I did
> that was so that the BFO could be a zero-beat when it was also at
> 455.000kc.  That may really be irrelevant but it was my reason.
> 
> I started looking at the STAGE GAIN procedures and when I injected the
> signal into the 6th IF amp's grid, I could tell that 455.000kc wasn't
> getting me the peak on the DIODE LOAD and, instead tha frequency is a
> few kc away from there so something isn't right about my setup;
> however, I'm still puzzled at why the IF chain can't be "forced" to be
> peaked right on 455kc.  Is this because there are some fixed values in
> the transformers and a "best" frequency is the best one can do with
> those fixed values? If not, then would someone please explain this to
> me as I'm still not making sense of it.
> 
> Thanks,
> Barry - N4BUQ
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