"ground" screw with lock washer?

[Adrian]

I'm curious and I have yet to find a sufficient answer.
Why is there a lockwasher beneath the ONE screw head at the main transformer bell housing at "ground" (also for the S.E.X. 2.1 I am just starting)?
I painted the bell housing and installed as designed but there is no mention that perhaps I should have ensured a good ground connection to the bell housing (e.g., scrape the paint to bare metal).
No paint scraping, no bare metal there and this thing sounds great.  Am I in trouble or does this even matter?

[Paul Joppa]

Probably the lock washer has penetrated the paint and made a connection; however I recommend you make sure.

The transformer core and end bell are in this way grounded, for reasons of safety as well as reduced hum. If the transformer should suffer an internal short, the ground connection will cause the fuse to blow, which is cheaper than electrocuting the user. Yes I think it's important!

Hum is the reason for a single point ground. If there are multiple points then there will be loops of conductor, which will result in currents around the loops because there are AC magnetic fields near the transformer. These "ground loops" increase the likelihood of hum.

[mcandmar]

You just answered your own question, one that puzzled me too at first.  That lock washer is there to ensure a good grounding to the cover should somebody decide to paint it.

[Adrian]

PJ:  Thank you.  I understand fully the ground loop reasoning as well as the safety of the equipment and ME.
This amp is so very quiet - absolutely no hum, static, buzz, etc. -while using very good isolation HPs that there is probably a ground connection at the lockwasher as you surmise.
However, I will take your sage advice and carefull loosen it to ensure a good connection is made.
Muchas gracias, senior.

[grausch]

I also have not scraped the paint off both of my Crack transformer bell and Stereoumour transformer bell and chokes. Other than loosening the screws, is there another way in which I can check for proper grounding of these items?