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

[Barry Scott]

I just checked and my IF deck peaks at 455090 Hz so I presume my
crystal is still good.  I need to recheck IF alignment, though, just
to make sure things are where they should be because I still have my
doubts...

Thanks,
Barry - N4BUQ

On Mon, Oct 21, 2024 at 1:50 AM Larry Haney <larry41gm2 at gmail.com> wrote:
>
> 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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