Hello,
I'm sorry for resurrecting an old build thread but I've just finished building a pair of EQNs and am having the same problem with both. I'm able to properly bias them with my scope but at the point of equal clipping, I'm getting low frequency oscillating and motorboating that changes with the location of RV5. By turning it CCW or CW the pitch of the oscillation changes. I'm able to get rid of this oscillation and noise if I turn RV5 CCW, but when I do so, the bias is all wrong and I get unequal clipping of a sine wave thru the unit. I'm in a Radial 500 series rackmount and when I unplug all other units, I still get the same problem.
All the controls of the EQ work great besides this unwanted noise and oscillation. I've double checked my transformer wiring and the resistor values around the output stage on the main boards and all seems well.
I would greatly appreciate any direction, thank you!