[R-390] Distortion

[Bill Smith]

Is this also a good procedure for the R-390?

73 de Bill, AB6MT
billsmith@ispwest.com

----- Original Message -----
From: "Roy Morgan" <roy.morgan@nist.gov>
To: "R-390 Reflector" <r-390@mailman.qth.net>
Sent: Monday, April 07, 2003 1:10 PM
Subject: Re: [R-390] Distortion


> At 10:14 PM 4/4/03 -0500, K2LNU wrote:
> >Hello R-390A Fans,
> >Can anyone tell me a probable cause for an R-390A going into distortion
when
> >the RF gain is turned up above 5?
>
> 1) Remove all tubes substituted for the originally specified ones in
> attempt to make the receiver "hotter". Replace with the correct
> tube(s).  Do not delude yourself in thinking that a higher gain tube is
> going to make the radio work better.
>
> 2) Make sure your IF gain adjust pot is not set too high.
> See chuck Rippel's site for the instructions on how to set it.
>
> <http://www.R390A.com/>
> specifically:
> <http://www.R390A.com/html/gain.html>
> Which I quote here to make it REALLY easy for any one wanting to do this
> (parentheses are mine):
>
> Procedure to set R390A IF Gain:
>
>   Once the receiver has been fully mechanically and electrically aligned,
> the final procedure to perform before "buttoning it up" is to set the IF
> gain control.
>   Many otherwise very sensitive R390A's are thought not to be due to weak
> signals being covered by noise generated by excess IF deck gain.
>
>                          Allow the receiver to warm up for at least 1 hour
> then:
>
>                          1- Terminate the antenna input (put 120 ohms
> across the balanced terminals, or ground one and put 50 ohms from the
other
> to ground)
>                          2- Set receiver for 15.2 mHz
>                          3- Set the "FUNCTION" control to MGC
>                          4- Select the 4kc filter with the "BANDWIDTH"
>                          5- Set "RF GAIN" control to 10 or maximum
>                          6- Peak the "ANTENNA TRIM" for maximum noise as
> indicated on the "LINE LEVEL" meter (If you get no peak you have other
> problems, most likely alignment.)
>                          7- Set "Line Meter" switch to -10db scale
>                          8- Set "Line Gain" control to full CW or "10."
>                          9- Adjust IF gain control, R-519 to cause "Line
> Level" meter to indicate between -4 to -7 VU.
>                         10- Re-zero the carrier meter control, R-523
>                         11- Set controls above for normal operation and
> reconnect antenna
>
>                         (12- Please report to the list what success you
had
> with this.)
>
> (What this does is set the IF gain so that with the audio and rf gain full
> up, you get a modest but discernable noise from the front end, the first
rf
> amplifier.  The overall gain of the radio is enough so you can hear any,
> repeat any signal that is just below, at or just above the noise of the
> radio itself.  And, the IF and AVC system can manage the gain of the
> various stages of the radio to keep distortion to a minimum.  Each stage
of
> the radio is pulling it's fair share with out being run at too much
> gain.  No stage overloads more than necessary or at a signal level lower
> than is optimum.)
>
> Roy
>
>
>
>
> - Roy Morgan, K1LKY since 1959 - Keep 'em Glowing!
> 7130 Panorama Drive, Derwood MD 20855
> Home: 301-330-8828 Work: Voice: 301-975-3254,  Fax: 301-948-6213
> roy.morgan@nist.gov --
>
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