[Heathkit] HW-101 low ouput on 40 - the Conclusion!

[Tony Brock-Fisher]

Well, after spending several weeks and loosing lots of hair and sleep over this pesky HW-101, I found the answer this morning.

Symptom: Low output on 40 meters, only when coil cover installed. Output OK all bands with coil cover removed.

Cause: T1 tuned to wrong peak. Was tuned to peak with slug closest to chassis; output restored when tuned with slug to peak away from chassis.

Analysis: The symptom of low output on only one band was a red herring, as was the issue of the coil cover being removed. Actually, it was low drive on all bands. When the coil cover is removed, there's enough positive feedback around the driver stage to recover the lost drive - EXCEPT on 40. Once this symptom was ignored, regular troubleshooting discipline and comparison with a working rig quickly lead to the point where the signal was being lost, at T1. Also note that with the coil cover removed, the driver peak on transmit was shifted from the preselector peak on receive, and the circuit was very sensitivie, like it had to much Q. In effect, it was like having a Q-multiplier around the driver stage!

Thanks to all who made suggestions!!!


-Tony, K1KP