Linn LP 12 hum not coming from Bryton phono stage.

What I was getting at is whether the hum is due to a direct interaction between the cartridge and the TT motor.  One manifestation of that would be that the hum is loudest when the cartridge is nearest to the motor.

I'd start by checking the headshell wires of the K9.

Sometimes they can get too close to other pins. If so you could try to move them with a small non-metal implement like a toothpick etc. Just to see what happens to the hum.

You could also check the mains cable by moving it to see if that has an effect. Loose connections are notorious for causing hum issues.

As for the Valhalla board, I would not recommend an examination. It carries lethal voltages and you would also risk disturbing the suspension. Without the correct suspension setup, the sound of an LP12 collapses pitifully.

It might well be possible that the thin earth lead which grounds the sub-chassis may have strayed a little and is now picking up something from one of the board's high voltage components.

In this case you will be better off getting it checked by someone who has the required setup jig. They'd be able to take a closer look and give it a service and oil change etc at the same time.

I'm also far from convinced that the Linn belongs on a wall shelf. It's suspension can cope remarkably well with vertical resonances sat on a table, but not so well on a shelf with resonances coming from a wall.

However this is what I found some 15 - 20 years ago. Linn may have changed the suspension components a few times since. You should definitely consider ringing a dealer or maybe ringing Linn themselves. Sending an email certainly won't hurt either.

Turntable hum is the nightmare of every vinyl enthusiast, so the best of luck in getting it fixed 

Well, this is getting exciting!
I assume they tested the Sondek and gave it a clean bill of hum-less health. So something’s got to be up with your phono amp. You need to test this with a different phono. Buy a Schiit Mani on Amazon for $149. Or even a $30 cheapo unit. You can return it or use for another table.

@masi61 Sorry to hear of your continuing issues...this hobby can be more than frustrating at times!

Since Thomas OK set up your table ( which with the new upgrades should be stellar), I would not expect any issues with the table. OTOH, hum is usually caused by an improper grounding scheme. You should be sure that the Bryston and the tonearm phono cables are grounded through your preamp...( making sure that the connections are clean and good on the grounding wire!). If the problem persists, i would check and see if the phono stage is grounded and if the preamp is likewise.
If the hum is still an issue ( and it sounds like it might not be hum at this point), then i would be tempted to have the Bryston looked at by a Bryston rep. One other thing, if I remember correctly from the time i was listening to the Bryston, it has dip switches inside it to adjust the gain, you should make sure these are set for the value of your new cartridge!