HELP!

i'm searching for the specs of my amp
it's an old beaten up Marlboro GBO 15-B
i want to know when it was built, the productiondate
an if anyone coeld find out, the scematics

it has a realy crappy sound so i want to fix it ^^
also when i play with heavy base the volume keeps fading

so if anyone coeld help me, i'd be verry thankfull!!

greetings from holland!

Meaux