Korg Nutube B1 Line Build, I need some help....

[Manolo47]

Greetings: Built it last year for a friend. When finished it produced an intermittent whistle type noise in both channels simultaneously which I thought I had solved by taking and applying all your advices set forth in my consultation on this forum at that time. I thought it had been solved by making sure the PCB outer trace where the 4 bolts are, was connected electrically to the chassis.A few days ago my friend brought it to me because the same noise was being produced again in the right channel. It comes on after a few hours of playing time and if I press or touch the chassis it goes away, as well if I press the “tube” case. Later on the whistle starts again....so I’m including photos of the built to see if anyone of you catches something amiss. Thanks in advanced.

 

[Zen Mod]

twisted pairs - newer twist together two channel hots

you can and it is advisable to twist only natural pair of conductors - that being channel hot wire and channel GND wire

so - rewire that thing properly, hoping that susceptibility to oscillation will go down

to ensure that, remove those common gnd wires between RCAs and operate with twisted pairs

 

[Logic800]

Plus, not certain that the aluminium foil on top of the NuTube is a good idea, as it might be adding capacitive coupling where it's not needed.

 

[Manolo47]

This is what it took

I hope it helds... ‘been working ok without the whistle for many hours now.
2 blobs of blue tack did it. Don’t know about that “tube” something must be wrong with it to need that. Also took care of recommendations. Thanks.

 

[Logic800]

Excellent. Many people have put a double-sided adhesive foam pad under the NuTube, difficult to see if you have.