Audio Systems: Electronic organ, filter caps, earth ground

Question
Hello,
I own a 30 year old electronic organ that I am completely restoring.  Despite my best efforts, there remains a hum in the speakers.  All filter caps and grounds etc. have been replaced and painstakingly checked.  No ground loops exist, but the hum still remains.  I suspect there may be a short in the power transformer.  The instrument is not normally connected to an earth ground.  When I connect a multimeter from the organ chassis to an earth ground, with the organ 'on' I get an AC reading of aprox 67 volts, and aprox 150 millivolts AC with the organ OFF.  Grounding the organ chassis to earth has NO effect whatsoever on the hum.
Do I have a short in the transformer?

Answer
No, it is not the transformer.

You might try reversing the power cord; 30 years ago they did not always follow today's convention for wiring.

Also, try grounding the chassis and the electronic circuit grounds together.

Let me know if these tactics do not solve the problem.

C