One speaker just hums, no sound

You do not need to replace the whole back plate. First verify that the bias power supply is in fact the problem by swapping the left channel backplate with the right channel. Then take pictures of the back backplate and email them to Dr West. He will guide you in the diagnostic process. He will look for the spare components that you need to replace and ship them to you if you choose not to send the whole backplate in for repair at the factory.

Hi Jay,

The newer bias supplies should be a drop in replacement.
Again, speak to Connie at the factory
and she should be able to guide you accordingly.

Good luck!
John

Most likely the bias supply is defective, I would contact the factory for further advice and obtaining a replacement supply.
You might want to replace the bias supply in both backplates with the latest version as the supplies are now regulated and will maintain proper bias regardless of line voltage variations.

John

I would check the high voltage transformer is properly plugged in to the high voltage box. Then, check that the other wire coming from that transformer is secured to ground.