After replacing the rest of the TL072 IC's, and added 0.1uF Monolythic ceramic bypass caps across U7 and U2, that made no difference. Powering the Preamp PCB externally, looking at U7A, that oscillation is STIFF. I've swapped op amps, changed types (tried NJR 4560D's in U7, U8 & U9 with no difference. I ran out of time while digging for replacement 3.3nF caps and 10.0k resistors to swap out those in the State Variable Filter that lives in U7/U8 stages. Removing U8, as one might expect, eliminated the oscillation at U7A. I didn't have any 3.3nF, so will use 2.2nF and 15.0k to set it to the same frequency when I get in tomorrow morning.