frequency response is "very interesting":
picture shows the FR with treble + bass turned to center position.
So it seems the bass control will have to increase the bass response
and the treble pot has to be turned to minimum. The best results are
with the bass control turned to the pilot light and the treble
control to the minimum position.
frequency response still depends on the volume pot:
Upper left: Volume
turned to pilot light (90°)
Upper right: Volume
turned to the right (180°)
Lower left: Volume
Lower right: As before
with treble in center.
You see, this
amp makes it interesting finding a "linear" response....
Otherwise it is
a nice base to get a linear working power amp when bypassing the
tone and volume controls.