I found one at a good price. I havn´t bought it ´cause I want to know: 1) How much does it weight? Heavy? Is it worth the effort? 2) How long can I play it without changing the tubes (if they are new)? 3) What shall I watch out for when buying a used one? I´m a bit scared of tubes and the fact that they are so expensive and can break in the middel of a gig. How fragile are they???