Setup:

CE 20A to dummy load
1 KHz audio input tone
scope accross the output of the phase shift network ( 90 deg shift)

Observation:

The X-Y scope display shows a very nice circle which varies in diameter with
the amplitude of the input and also varies in diameter (although less
variation) with the input frequency. The inside of the circle always looks
to be a well defined circle but the thickness of the line has some variation
around the circumference. Thin and sharp at 6:00 thru 10:00 and a little
thicker from 12:00 to 2:00.

The two signals look great in the time domain just like two sine waves out
of phase.

Question:

Is there something going on that needs correction?

K3PID
Ron H.