Need Help w/ 100 watt linear audio amplifier

I'm building a 100 watt amp with an RCA 2000H. I put some pictures and description on my web site:

**broken link removed**

Can anyone help me diagnose why I'm getting the MHz noise and distortion at higher output levels?

I was planning to describe the construction details more, but haven't had time. I can easily take more pictures and put up some descriptions if helpful.

I tied all the grounds together, AC in, load, and signal.

Any thoughts or suggestions? Need more info?

Thanks,
Max

Resistor substitution boxes have a lot of capacitance. Capacitance from the inverting input to GND can cause the amplifier to oscillate. Try replacing the box with a potentiometer (wired as a rheostat), with leads as short as possible. This includes the leads to the capacitor that is in series with the pot.
Have you included generous power supply bypass caps, also with short leads?

Not Sure how you tied All the Ground Together, But That can cause "Ground Loops" if done Improperly. That will Result in Oscillations.

Also Depending on the Over-all gain, Resistive or Diode de-coupling can also be important.

Gary