[Halsol]

The loss of signal below 800 KHZ may be due to the variable condenser having warped plates that touch causing a shorting out and loss of signal. I found it not unusual for this to happen. It is around this point where the greater amount of meshing occurs between the plates. If the moveable plates comes in contact with the stationary plates of the tuning condenser you may hear intermittent scratching or experience complete signal loss. A close examination under good light with the aid of a magnifying glass may be of help.
Hal