[R-390] R-390A Audio hiss

[Roy Morgan]

At 11:04 AM 8/30/03 -0400, you wrote:
..  I have a very
>objectionable hiss from the spkr constantly.  Can
>anyone tell me what I'm doing wrong??

Joe,

Adjust the IF gain setting..

It is very common for folks who don't understand to set the IF GAIN 
adjustment too high. They think it "makes the receiver hotter."  It is a 
mistake. (It is also a mistake to put higher gain tubes in place of the 
normal ones..Check that you have the correct tubes installed, especially 
the 6DC6 in the first RF amplifier.)

Here is the IF Gain set procedure:


IF GAIN SETTING

Here is Chuck's procedure:
From: http://www.R390A.com/html/gain.html>
Text in brackets [ ... ] is mine (Roy, K1LKY)
*********************
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 [minus 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 [This can be a touchy 
adjustment.]
  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 --