[R-390] Distortion

[Jim Brannigan]

Generally, it is a good procedure for all receivers.
The first stage should set the noise level for the entire receiver.  If a
signal won't pass the threshold of first stage it won't be heard.

from a snowy NY (in April, Grrrrr)
Jim

> 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