Inner side of the lugs showing the internal wire between hf ground and +24v (red and orange wires) https://assets.chaos.social/media_attachments/files/113/800/586/669/361/221/original/6e7792bef978fde0.jpg
@altomare starting analysis of the second board. As suspected, the coax shield is connected to the positive supply, so this oscillator is actually powered by -24VDC to ground... Or, output signal is referenced to +24V. Weird.