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

[Larry Haney]

Hi Barry,  The reason is that the 390 and 390A have crystal filters at the
front of the IF circuit.  The idea is to use the frequency that the crystal
has drifted to as long as it has not drifted too much (which would be about
300 cycles, but that is arbitrary).  And this is mostly so that cw
reception (.1 and 1 kc bandwidth) can be at its best.  If you don't care
about cw, then your choice is to live with it or replace it.

Regards, Larry

On Sun, Oct 20, 2024 at 5:09 PM Barry Scott <72volkswagon at gmail.com> wrote:

> 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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