Used tubes question

Thanks everyone.
Any suggestions on what to look for in a tube tester? And, will testing tubes keep me from damaging my amp? What should I be on the look out, or, ear out for, when I turn the amp on that might signify a problem? Distortion? Weird tube colors? 10 foot flames?
Thanks again.

They sound fan-f*ing-tastic. Wow. I'm going to save up for a NOS pair or two. Wow, wow, wow....

Borders on a musical epiphany, does it not? As Trelja noted: The built quality back then was much better than that exhibited in today's manufacturing. Try to locate either TungSol or Sylvania 6CS7 dual triodes, for the preamp section(must be closely matched pairs and low noise). Small signal tubes have a major effect on presentation. Many don't realize how much can be gained with a NOS tube in the power supply. Replace that 6CJ3 rectifier for even more musical enjoyment. Welcome to the wonderful world of tube rolling. Happy listening!! =8^)

Yes. Yes. Yes.
I've removed the tubes from the amp and encased them in 20 layers of silk velvet. I'm thinking I will only put them in for special occasions. Why waste them on the kids when they are listening to Dan Zanes! No disrespect to the very talented Mr. Zanes intended.
I guess I should just find a NOS quad.
I just ordered some Sylvania 6CS7's today. What about RCA 6CS7's? Do you know of a source for Tung Sol 6CS7's? Really, the rectifier will make that much difference?

Finding TungSols in matched pairs will be hard to do(no- I can't cite a good source), but worth the effort if you can locate some that are low enough noise for a preamp section. Depending on what half wave rectifier you are presently using(ie: Chinese), you should have an audible improvement by installing say, a NOS RCA. They're selling for around $5 now, so the experiment will be cheap. Too bad there aren't any Mullards out there.