Talkien>> there is no real way to test whether the tubes actually work fine, but you can do a basic test to check if the tube is a dud or not. You would see the filament in the tube right? the tube would have a number of points depending on whether its a triode , quatrode, double diode, pentode etc. trace the two points connecting the filament. Usually shops selling tubes should have a 6V supply with them. connect the supply and make sure the filament glows. Or connect a multimeter and check continuity. This will ensure you don't take home a dud, but I guess the sound etc will differ from make to make. Thankfully in Bangalore we do get plenty of matched tubes.
Now, to help a fellow guitarist out, would you like to tell me a bit about the output transformer? Like maybe the ratings and turns ratio and type of wire & core used etc, so I can get one made here? I would be really grateful. I'm talking of the big transformer at the end, right after the main amp output tubes. Thanks in advance, expecting a response or PM.
PS: I can help you with buying tubes here in return if you want.
Ibanez GSR390 Bass guitar (might sell if i get a price)
Laney RB30 Bass amp (might sell if i get a price)
Bunch of Boss pedals