In my experiance the 5150 range had quite a bad rep, I played one once and wasn't overly fussed, not the most vesatile amps but there a re worse...much worse. Like I said earlier though anything witha valve in it is going to rock your world at the mo'.
Beacause of this they tend to go for cheap on EBay. Byy using Paypal and you are well covered, if it doesn't work, if it isn't your kind of amp sell it on.