I have a PF500. I run an ART Tube MP Project Series from my tuner out to the effects loop in and blend it in with the PF's EQ'd signal using the blend knob. I'm going to experiment with some different tubes, (ECC82 for example), I just copped off TB classifieds. Got the ART the same way, like new, original box and O/M, 45 beans. I have fun tweaking new sounds. Enjoy.