Used tubes question

I bought a used quad of xf2's. They were cheap, 150.00 bucks, so I figured I'd give this older-mullard-tube-thing one reads about so much a listen. Now I worry about putting them in my intergrated. I have a Leben CS-600 and fear it going up in flames. The seller said they were closely matched and tested on his such and such tester. He had plenty of positive feedback. Should I just pop 'em in and see what happens? What is the worst that can happen?
I would actually try to get them tested first if possible..Even if its for peace of mind and cost a few bucks.I have even had NOS tubes that tested perfect go bad after 30 minutes of play time. I don't go out of my system area for at least a couple hours on first start up,just in case a tube wiggs out, your there to shut down as quick as possible...Thats what I do anyway.......
I would sacrifice the sound quality or pay more, but buy stock factory brand new tubes. Same with TT cartridges NIB only period.
but buy stock factory brand new tubes

IMO ,I totally disagree..Ive bought tons of used tubes on ebay with no issues.Mullards,Seimens etc etc,Seems rather silly to spend twice the money from a tube broker or buy inferior "new" tubes when the real deal stuff is available on the bay.Get a tube tester.They are everywhere,cheap enough and its kindof fun to test them..
Given the seller's good feedback, I suspect you'll be fine. I too have bought lots of old tubes with no real issues.

Old signal tubes rule.
Agree with Steidlguitars.

Buying old used tubes is a good way to go. I've been particularly lucky along these lines.

Normally, these older tubes have held up very well over time, a tribute to build quality which is not replicated today. If you can give up the snob factor of NOS, there are some real gems to be found at comfortable pricing.
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.
I only use NOS tubes and there are big differences between these even in the Mullard variety. I switched from Phillips miniwatt 6GW8 for my Rogers Cadet III to English Mullard NOS. I am finding these harder to source but I hunt them down. Massive improvement. Good NOS rectifiers will improve things further. Lebens are respectable little amps and contrary to common misconceptions quite robust. The only thing is the Leben fixed or cathode bias if the latter pop em in and enjoy. Cheers
Wow again. What a difference with the Sylvania 6CS7's. It is more dramatic then when I added the xf2's. BTW-The CS-600 is more than respectable and more than little :-).
Those that don't experiment with NOS tubes, just don't know what they're missing. Enjoy your music!! =8^)