[Hallicrafters] SX-111 RF align noise

[Roy Morgan]

At 08:01 AM 4/17/2004 -0400, you wrote:
>Hello all,
>  Besides touching it, can anyone tell me what I'm doing wrong? I am 
> trying to align the rf on an SX-111.
>My best efforts seem to make it prone to internal noise. Peaking the rf 
>section to maximum per the manual brings the noise to abt S-7, S-9. 
>...  any suggestions ...


1) Is there a way to set the IF gain? If so do it. You also may have the 
S-meter adjustment way up.  If the noise is normal and the S-meter is not 
measuring correctly, you'll get a high reading on perfectly normal 
noise.  50 micro volts for S-9 is a common set point.

2) Are there any non-standard tubes in the radio? E.g. a 6AH6 in stead of a 
6AU6?  Any high gain tubes installed to make the receiver "hotter" should 
be replaced with the original type.

3) Check screen dropping resistors in the RF and IF section for noise by 
bypassing the existing bypass cap with another one: disk ceramic or foil of 
similar or higher capacitance with small alligator clips on it serve well. 
You are checking for open bypass caps and noisy resistors all at once.

4) Short each grid in the signal path to ground one by one to isolate the 
source of the noise.

5) Replace each tube in the RF section with another one, preferably one 
which is working ok but has hours on it.. not a new tube.  New tubes are 
known to have higher internal noise that ones "broken in" for a while.

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
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