How to clean inside Amps and PreAmps

I would put the covers back on as well. Then cover as you have been. Why did you remove the covers? If they are SS you are not doing yourself any favors. Sometimes the lids are integral to the heat sink operation and need to be present. Be careful and what is microdust? Can you see it with the naked eye?

I have ARC Ref 5SE preamp and REF 250 AMPs and read many posts they sound good without covers . Also removing covers was dissipating heat faster than built in fans.

I remove the cover on my SS amp, and keep it off.
We all have to breathe (especially when pets and small children
are not present.) I concur to a draped cloth when not in use.

Occasionally I apply some anti-static spray
(3M, for example) to the end of a small
acid-free brush (electronic or art supply store).
Apply spray to brush when you are away from amp.
When the brush is moist but not dripping wet, dust
treated areas slowly with a light stroke. A small brush can get
into crevices neatly. Reapply spray as needed.

You will see and hear a substantial difference!
Re-treat as needed. Anti-static spray has other useful
applications... try wiping a sprayed microfiber cloth
on the outside of components, cables, shelves, and racks.

If you are going to clean the inside of your equipment, please unplug the items first. This is obvious, but needed to be said. Dust will collect, so occasional cleaning is really necessary, but do so safely. Non conductive brushes (still unplugged mind you), is a good idea.

enjoy

The best way to clean solid state equipment is to throw it into a lake and let it lay on the bottom for a couple of years. In the meantime, replace all of the equipment that now sits on the bottom of the lake with good quality vacuum tube equipment. All other responses above apply. :>)