Re: 5150 block letter opinions?
Expect to pay between $600 and $700 these days, in solid condition. These amps are absolute workhorses and will survive one hell of a beating, so most of them have tolex in not-so-great shape.
Don't let anyone tell you the block letters sound better than the signature heads - they shipped from factory with different tubes, and that's literally the only difference.
In all honesty, the 5150 is my favorite head. There's a reason I've had 4 of them and keep coming back for more!