Hi everyone  :tu: my first day and first post !   a while back I was given a Yamaha hundred B212 from the early 80's I think, it was working but the volume was very low.I finally got round to taking a look today, first thing I noticed was the speakers, the originals were had been replaced (2x 60watt 8ohm yams) instead it had 2x 400watt 4ohm subwoofers !!!! (the amp is rated at 4ohm) now even my dumb brain knows that aint good lol, no way to match the impedance !  so I hunted round and found 2 tweeters rated 100watt 4 ohms, so hooking them to the subs in series/parallel would give me 4ohms 
Checked polarity etc made sure all 4 were working and gave it a go.
it sounded really good ! just about perfect as I play mostly acoustic,I was sitting playing and feeling smug then tried to crank it up a bit..... same as before  very low volume. Seems about half of what it should be (its a 100watt amp btw)
Only other thing I can find is one channel is off and buzzes like mad. the other channel works great, nice and clear on both high and low inputs but I'm guessing this has nothing to do with the problem (I do a lot of guessing lol)
Any ideas guys ?