[R-390] R-390A trouble

[Roy Morgan]

At 03:15 PM 3/28/02 -0500, Jim Temple wrote:
>Hi Roger and list,
>
>OK, here is what I found.  (Narrowing down the sypmtoms).
>
>1.  In AGC position.
>     a.  RF gain at 5.  AGC voltage essentially 0.  Little rushing sound.
>Receiver apparently stable.
>     b.  As RF gain is increased, background/rushing noise slowly increases
>to a level that seems normal and strong.  Noise sounds normal and stable.
>TO A POINT.
>     c.  As RF gain increases toward 9, the AGC voltage abruptly increases
>and the audio breaks into the putt, putt/screeching sound.


Your overall receiver gain is way too high.

The noise from the receiver should be moderate to low with af gain way up 
and rf gain way up and the antenna connector loaded with some appropriate 
dummy load like 50 or 125 ohms.

It seems to me that the normal receiver front end noise should not cause 
the AGC voltage to rise.

Did you set the IF gain with the procedure on Chuch Rippel's site?
Did you put a 6DC6 tube in the front end? (you do NOT need any "hotter" 
tube in there!)
Have you got the normal tubes in all the other sockets?
Have you looked at the IF output on a scope to see what is happening there?
Have you looked at the AGC voltage on a meter or better yet on a scope to 
see what is happening?
Have you pulled out one tube at a time beginning at the first rf amplifier 
to find out where this is occurring?
Have you measured the resistance from ground to the wiper of the RF Gain 
control as you rotate it to see if it has an open spot?
Have you put some Caig MCL into that control to make it operate smoothly?

Here is Chuck's procedure:
From: http://www.R390A.com/html/gain.html>
Text in brackets [ ... ] is 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. [This means that you should have done the mechanical 
alignment - set the cams properly and so on.]
  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 [This means unhook any antenna and put a 
50 ohm resistor,or a 125 ohm resistor, on the balanced antenna input, no 
signals from any antenna or signal generator.]
  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 [If your receiver goes whacko 
at this point, reduce the IF gain setting as in step 9 till it behaves right.]
  6- Peak the "ANTENNA TRIM" for maximum noise as indicated on the "LINE 
LEVEL" meter [If you do not get a noticeable peak, your receivers front end 
and rf amplifier stages are not working right.]
  7- Set "Line Meter" switch to -10db scale [mknus 10 db]
  8- Set "Line Gain" control to full CW or "10." [Local Audio gain 0 or low 
if you are listening to it.]
  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

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 --