Static stain cleaning

[Tubesin]

Hello,
May you help me on how to clean the static stain on the aluminum face plate of the SP11 preamplifier? I tried with electronic solvent, W40 and carwax but only lighten up and cannot clean it completely.
Thanks your helping hands.😕
Attaching a photo

 

[kevinkr]

I would contact ARC directly and find out what the finish on the front panel actually is, and how to safely clean it. It is probable that there is a lacquer or some other type of finish on the aluminum, and it could even be that this has become discolored over time due to heat and air pollution..

Kevin

 

[Tubesin]

So... it might be the lacquer or the protection coating is oxidized then....