Debuzzing a Wheaton TriPlanar problem

Dr_John, I think I did not read your first post all that clearly. Now the problem sounds to me like it might be a sort of RF oscillation in the preamp. I would not characterize this as 'feedback'... it sounds like either a very bad ground or RF in the system. The fact that you can touch the arm tube and have the sound go away for extended times suggests that its an RF problem. I don't think its anything with the Cardas cable, as when you touch the arm tube, you should at that time be able to keep the arm still.

ok - another piece of evidence to add, and this may be the most telling. When I grasp the finger rest at the end of the tube, the hum gets really loud. Just squeezing the tube itself ever so lightly stops the noise. And this part baffles me - all I can think of is a defect in the cartridge.

RFI/EMI problems at tonearm wires can tend to jump around unpredictably as you describe and vary in proximity with the human body. Grounding the tonearm or TT is sometimes not enough, and screened tonearm wire may be necessary to resolve the problem.

Does the hum continue when the cartridge pins are disconnected from the tonearm wires?

You might experiment by relocating the TT to another part of the room. The current location may be in a bad RFI field or too close to in-wall AC wiring or to the AC PS of another component.

Now this is making more sense to me, and I thank you. The TT is 6 inches from the wall which conceals all the electrical lines from the apartment's circuit breaker. And I must ask what is 'screened tonearm wire' ? I want to try this fix before relocating the equipment rack. Thanks.

Based on your responses to Dave and Ralph, I am now thinking that I got it wrong. Am I now correct in thinking that the tonearm per se is not necessarily vibrating but that the hum you hear (over the speakers, I presume) is ameliorated when you grasp the arm tube? If so, this makes much more sense, and I agree with Dave. But I will throw in another idea; the arm tube structure is grounded to the arm pivot (i.e., makes electrical contact with) the bearings only. I once had a maddening hum problem that was only cured when I took my tonearm to Herb Papier (the inventor and original manufacturer). Herb lived about 10 miles from my house. Herb took my arm, and before my eyes he tightened the bearings by a hair, and the problem was gone. That has to have been nearly 20 years ago, and I have had no recurrence of the problem. Problem is you need a Herb or a Tri to do it so as not to over-tighten the bearings.