Eliminate hum in headphone amp

I have a tube/valve headphone amp with a separate power and amplification unit. I do love the amp, but if I place the two parts too close together, there is an audible hum in the background.

These units are of course attached with what appears to be a short proprietary umbilical cable. The obvious answer would be keep them apart, but the cable is too short to not induce stresses and have no noise.

I tried a ferrite choke as I had some on hand. No joy.

Any thoughts? Needing to move them back and forth based on if I’m going to use it, is not ideal.

Have you tried running a ground wire from each piece to an earth ground? Tubes hum. Unfortunately. I had a Woo tube headphone amp that I sold because I couldn’t get the hum out. If you get it sorted please come back and share the solution.

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I am using a Woo. The only way I can get it to stop, so far, is to move the pieces apart.
Line conditioner, chokes etc.
They have to be separated. Then, no hum.

I will run a line to my earth ground.

Not in the same league as a Woo, but I had a Little Dot that I gave up listening to because of hum. Only on the headphone circuit, but not when using it as a pre-amp.

So, in my case and maybe yours, I am blaming a bad solder somewhere.

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Doesn’t sound like any sort of grounding or loose solder joint problem, but rather like a mains transformer with too large a stray field.
It either needs a Mu-Metal cover or a longer power supply umbilical to place it far enough away.
Probably not an option, but rotating the PS 90 degrees in one of the three axes might help…

I can rotate the power block and see. I will next time I have the chance.
Mu-Metal. I am going to give that a good read too.
Thank you.