Tube amps are more expensive than their solid-state brethren, there's no way around it. What budget are you looking at?

I've started seeing Fender Blues Juniors on the market for around $400. That's a good amp for the money (I gig with one for smaller gigs) and the 5 year transferable warranty doesn't hurt. There are plenty of baby tube Fenders in the used shops; hunt around and you should find a bargain.

Also, look for used Gibson tube amps. For some reason, old Gibson amps are still a good bargain (especially when compared to similar-vintage Fender amps!) and they have a gorgeous tone. There's also the Traynor 20-watt amp, which is a 3-channel tube amp with reverb. Good deal, and sounds great as well. A buddy of mine recently bought one, and I was very impressed with it tonally.

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General of the Grammar Nazis, 41st Exploding Toad Division.