Grundig Yacht Boy 209N (1969) - distortion

[paulsherwin]

I'd bought this set from a dealer, apparently untouched internally and unused since the 70s. It worked very well except for a high level of audio distortion on all wavebands and stations, which I certainly didn't expect in a set of this quality.

My initial assumption was that this was a capacitor problem, so I changed all the electrolytics (there aren't that many). This made no difference at all, so I decided an AF realignment was needed. The audio stages have lots of presets, all undocumented except R52 which sets the quiescent current. Given the level of distortion I thought it would be unlikely that the quiescent current had just drifted off a bit, but I had no idea how to do a complete factory realignment. The official Grundig service manual certainly doesn't explain how to do it. I put the radio on one side for a few months and worked on other things.

Eventually I decided to check the quiescent current, which should be 5.5mA. It was 550 uA! Somebody, possibly in the Grundig factory in Portugal, had had the test meter on the wrong range when setting the current. I wonder how many of these sets went out of the factory with misaligned output stages before quality control picked it up?

Anyway, I adjusted R52 to give the correct 5.5mA reading and the radio sounds fine now.

Best regards,
Paul