The ripple shouldn't be 60 Hz, more like 30 to 60 Khz or so.  Tek used oscillators to minimize HV transformer weight and size.  I've had issues with parts where the probe touching the circuit makes it work beautifully.  That turned out to be a floating lead that I hadn't connected (IIRC).  probe loading would make it look like ground for a bit.  Those would be the HV filter capacitors, so looking at them with an HV probe could be helpful.

The higher the frequency, the more effective a smaller value of cap will be.  Some old scopes that ran the CRT off 60 Hz high voltage used some very large (and nasty) filter capacitors to keep ripple down.

Harvey