Eliminate system hum

I found getting an electrician to install a dedicated line, to get my hi-fi isolated from TV and other appliances, was a very cost-effective solution to transformer hum. It cost much less than decent power conditioners, which may or may not provide other benefits.

That said, I also found that speaker cable with the correct impedance for my particular amp (not a tube amp) made a big difference. Installing unsuitable cable, even though it sounded good in other ways, brought back transformer hum.
Removing it eliminated the problem. Your dealer or manufacturer rep may have useful information on impedance matching between cable and amp. Good luck!

-paul-

I have found several brands of EF86 tubes are very sensitive to RF noise. Make sure its not any of the tubes by moving your hand close to them,(do not touch them) if the noise level changes then try another tube.

If you have a Tube Cage, try taking it off or if your not using it putting it on.

You dont say if your using any power conditioning, if you are, try lifting the ground on the amp by using a cheater plug. This might indicate a ground loop.

Try a better power cord on your amp. Perhaps one with better shielding.

I have used the Blue Circle Noise Hound with EXCELLENT results. Just plug it in to any outlet close to the outlets that you use for your tv.

PS Audio makes a humbuster. No personal experience though.

A dedicated circuit is the best way to go. The Nation Elec.Code (NEC) has changed it's grounding requirements over the years. So it depends when you house was built or updated what kind of grounding you have. Also different States ,Counties and Cities have varying requirements. What you need is a dedicated ground and neutral to your System. The neutral is a current carring ground. It will transfer noise. Also if your electrical panel has a bonded ground the neutral and ground are connected at that point (carries noise). You need to "float" your ground to your music system. Talk to your electrician when installing a dedicated circuit about isolating you neutral and mechanical ground.

NEVER use a cheater plug!!!!

That is extremely dangerous and does not provide a way for parasitic currents to ground. Believe me you do not want to be the path to ground!!!

The answer is to ground all equipment in the system to a common potential i.e. a single circuit or circuits that use a common ground.