HRO 60 Noise Limiter

[WA9ZBW]

I have an HRO 60 that has developed an interesting problem.  When the the receiver noise limiter is turned OFF, the audio has become very weak and mushy.  When I turn the noise limiter to the ON position, the audio is normal in both volume and quality.

So far I have been checking components in the V12 and V13 circuits and have replaced a few resistors and a caps that were out of spec, but still no change.  I have also swapped both tubes with no change.  Quite a few of the caps have been updated with orange dipped ones, so the chassis is a mixture of original and new parts.

Has anyone seen this before and/or have any suggestions?

Thanks, John WA9ZBW

[WQ9E]

John,

Check to make sure the switch itself isn't the problem.  Measure to see whether the common connection of R-37 and R-35 is grounded when the switch is off. 

[K3ZS]

I have had the same problem with a different receiver.    It was the switch.    Toggle it back and forth a bunch of times to see if the audio comes back on.

[KM1H]

The HRO-60 I did a few months ago required replacing every paper cap, electrolytics, and over 20 resistors to get it working as designed.

In your particular case there are probably leaky caps on the AGC line and the NL circuit partially compensates for it as both circuits share a few common components.

Doing anything less than a complete job is simply wasting time.

Carl
KM1H

[WA9ZBW]

Thanks Roger, Bob and Carl for your suggestions.  What helped me was the suggestions of checking the noise limiter switch.  The switch checked OK but in the troubleshooting process I decided to test all parts tied to the switching line and found that R38 was completely open!  That was what was messing up the audio amp V13 when the noise limiter was off.  Works normal now.

Thanks again, John WA9ZBW