The A5 was part of the "A Series" Pioneer components, manufactured starting about 1980. I don't recall what the output of the A-5 was but by its place in the line, it should be about 40-50 watts per channel into 8 ohms.
The output section of the A Series amps employed a circuit topology which Pioneer called a "non-switching amp" design. It was their name for the same topology used by a few other manufacturers at the time including Nikko, variously called "sliding bias", "dynamic bias," and "new class A." Whatever the name, this topology was claimed to provide the benefits of class A operation without the heat generation and requirement of massive heatsinks.
The A Series components were a departure from Pioneer's traditional silver and featured a gold finish with green display. I owned a model A-8 integrated amp (90 w.p.c) and SR-9 reverb amp (also part of the A Series). I still own an SR-9 today, though not the original one from back in the day.
Some of Pioneer A Series:
http://www.audiokarma.org/gallery/showphoto.php?photo=405&password=&sort=1&cat=507&page=10
My SR-9:
