Tube amps are something I have yet to try, and am planning on buying the grandaddy of them all.....the almighty SVT. I know very little about these, and would like some input on where to start, and the differences between the different eras. I am looking to get: 60's-70's SVT, 80's model SVT, or maybe even the current SVT CL (classic) head. What are the ups and downs of each? Thanks in advance!