Transformer rating ?

[woody]

I have some questions on transformer ratings and temperature rise as they relate to filliment transformers. For example I have
a 2.5V 3A fillimint transformer that gives me 2.8v without a load
and 2.4v when loaded at 3.4A. When I loaded this transformer at 3.4A it was just a little warm after an hour of use maby a 20 degree tempature rise. So I am wondering if the 3A rating is more of a design center rating than a maxium rating?

I have a 6.3v 15A filliment transformer marked Grade 1 Class A
I wonder what the grade 1 and class A refer to? I need to use it
at 17A but don't want it to fail after a week or so. But again when I overloaded it at 19A it was only babby bottle warm after an hour of use. On the other hand I have a controle transformer
that gets realy hot when loaded at 70% of it's rated current.