[Amps] transformer distortion question

[Drax Felton]

I'm making a low power MOSFET amplifier for 475kHz with an IRF510.   It 
works fairly well and looks nice on the scope, but now I'm trying to 
transformer couple its output to a second stage.

I made a center tapped,  bifiliar wound, toroid transformer out of 26 
turns of 22 ga. magnet wire on a 1" diameter core. This is so that I can 
split the phases to drive the second stage as a push-pull.

When I look at the output of the right side of the output of the 
transformer it looks like a perfect sine wave.When I look at the left 
side's output the negative dip looks distorted.

Will someone look at these photos of my oscilloscope and suggest what 
might be happening here?
Why is it only on one side of my transformer, only on the negative dip?

Scope:
https://dl.dropboxusercontent.com/u/24304293/transformer_distort.jpg



The transformer:
https://dl.dropboxusercontent.com/u/24304293/kb3x_475_amp.jpg
Both sides of the output are shunted to ground with 100 ohm resistors.  
The center tap is grounded.  The left side of the input is grounded and 
the right is the signal input.


Drax
KB3X