Wurlitzer Model 145 Electric Piano - Buzzing Sound

[Curts Dad]

My son has acquired a Wurlitzer Model 145 Electric Piano with a tube-type amplifier.  The piano plays fine, but has a persistent buzzing sound coming through the amplifier.  I am helping him troubleshoot via FaceTime as I am in Canada and he is in NYC.  The amplitude of the buzz can be controlled with the volume potentiometer and the frequency remains constant,  The buzz doesn't sound to be 60 Hz.  I walked him through a check of all grounding in the piano.  A couple of things were suspect but there was no change after minor repairs.  Any ideas for next steps?

I have a short .mp4 video of the problem that I can share on request.

Many thanks for your thoughts,

Dave

[mvanmanen]

Hi Dave. I have a 145 as well after I tried to add a three-prong plug it got noisy from a ground loop. Got rid of the three-prong plug and problem solved. One day I would like to ground it but it sounds more than quiet enough. Anyways...easy thing to try if it is the plug.

[pianotuner steveo]

This model came with a 2 prong plug originally. I don't think the plug is polarized. If not, tell him to try reversing the plug in the wall. If it is, a separate piece of one conducter wire can be wrapped along the power cable. Attach the amp side of this wire to the amp chassis. Attach the other side to the outlet plate screw, which is ground in a properly wired home. If not that, it could be a bad volume pot, a bad capacitor, or other issues. It could be the " death cap" but I don't want to open that can of worms until you rule out other things.

Always try the simplest things first. Especially if they don't cost anything!

[Curts Dad]

OK, have done additional troubleshooting using your advice.  Curt removed the ground wire from the three-prong plug and the buzz was attenuated significantly.  If he touches any of the metal portions of the piano with his finger it is again attenuated to (I think) fairly normal levels for this type of equipment.  If a ground wire from the electrical service is touched anywhere on the metal portions of the piano the buzz returns to the original levels.

I got Curt to make a brief YouTube video (link below) that demos this.  Further thoughts or "next steps" would be gratefully appreciated!

https://youtu.be/7LVkY8PV12M

[Curts Dad]

Hey pianotuner steveo, what are your thoughts on the attached picture that seems to show a capacitor from the main power input to the chassis of the amp?  Could this be the "death cap" that you wish not to speak?

Dave

[pianotuner steveo]

Yes, the round disc cap should be removed.