Extremely high ground noise: anyone encountered this before?

[Stabby]

I've got a Hohner Cembalet I (1959 electric piano) of which the ground part of the cable broke off. It uses tubes as can be seen on this picture:

http://i56.tinypic.com/a0jukh.jpg

When I connect it to an amplifier, the ground makes a huuge sound, at least 10x at loud as the notes that play. To be more specific: if I would crank up the volume for an acceptable level of the notes, the accompanied ground noise would destroy my speakers in a flash.

I fixed the cable and the noise is gone. However I'm still worried. Has anyone else experienced this with an old device or anything with tubes? Is it normal or is there most likely something wrong?

[firechief]

Sounds like you fixed the problem. Being "off ground" can cause terrible hum.
The most common cause has to do with the way the AC outlets are wired. There are some other possibilties, but the ground is there to bring the insturments chassis to the same electrical potential as that amp you plugged into. Your good to go.

[benb]

Yeah, that's to be expected with a missing ground connection between two pieces of equipment. As most any electric guitar player can tell you, when you've got a cable with a bad ground connection, the hum can be a lot louder than the instrument sound. This can be true for a solid-state amplifier or instrument as well as tube.