In article , "N_Cook"
wrote:

Peavey Prowler amp from 1999. All the 1/4 inch sockets and one , only, of
the valve bases , bad solder joints, reacted to the re-soldering process as
though the tags were made of stainless steel or had a grease/oil film over
them. What could have been the cause?

The causes of corrosion are many. I know you enjoy failure analysis as
an independent intellectual pursuit, but it isn't going to help you in
the repair. Salt air, cigarette smoke, corrosive flux used by an amateur
in a previous repair, they all have the same remedy: Remove and Replace
affected components.