how much tubes influence on the sound ???

hi friends .
im new in the tubes world all i know that there is alot of kinds of tubes .i have cary sli80 amp with devore nines speakers ,i bought my amp in seconed hand and i dont know when the tubes was replaced or .. , all i know i have this tubes in my cary sli80 :
2 6sn7 elctron tube made in china.
2 6922 sovtek made in russia.
4 output tube svetlana electron devices 6550 c made in russia.
2 5u4gbeh electro harmonix masde in russia.

i see on all the tubes in the top alittle black color on the tubes i remember this since i bought this cary sli80,
and sound is ok ,why is that color on my tubes or how can i know when to change them ?
another importent thing is in my topic question is the tubes really change the sound that everyone can feel the change even people that not audiophiles ? i ask that bcz my dealer sugeest me 2 tubes 6922 of EAT that coast toghter 350 $ and if i buy the others tubes that less importent to the sound then the pre tubes is 250$ for all others,is it worth this my cary sli 80 that is very averge amp for this lovely speakers (devore fidelity nines).

there is nice friend here in the forum that suggest me this tubes to my cary sli80:
2 Amperex 7308 input tubes pre ----> is this better then -->eat tubes 6922 ?
2 sylvania 1952 6sn7gt "badboys" pre driver
4 goldlion kt88 output tubes
2ge544 rectifier

how much this set of tubes will coast me ? and is my amp worth this investment (honestly pls) ???
thanks alot and sorry about my long questions i will be glad to hear alot response to my all questions and by the way i love this audiogon forum very nice people and proffesionals people here bye and good day :-}
When you replace power tubes (the 4 larger tubes on your amp) they should all be of the same manufacture, according to Cary. They will need to have the bias current adjusted when you do this. Cary makes and sells a meter (MD 300?) just for this purpose that simplifies the task (pretty easy to do). Changing the smaller signal tubes does not reqire bias adjustments, and will change the sound of your amp to a slight degree. In VAGUE GENERALITIES, the european NOS Siemans, Telefunkens, Mazdas, will sound tonally neuteral, and more detailed than what you currently have, while Mullards will sound warmer and fuller. The 6SN7's also do not require bias adjustments, Ken Rads will have good bass response, but may be microphonic, the Sylvanias you mentioned should sound pretty nice, Tung Sol round plates are neuteral, detailed and tonally accurate (but good luck finding a pair that isn't worn out). RCA's typically have a sweet midrange. Unless you have a tube tester, or access to one, buying these tubes online is an expensive crapshoot. Many people buy expensive tubes for themselves, use them for a year or so and then try to pawn them off on some sucker who hopefully won't know that he just paid a small fortune for worn out tubes. Buy from a reputable dealer, The Chinese tubes nowadays are actually pretty decent and very affordable if you want to go the cheaper route. In my equipment the smaller tubes last a year or so, and the power tubes last 3 years or so (your results may vary). Tube degradation is a gradual process that you may not even perceive, but you will notice the difference when you retube. Turn your bias adjustment DOWN before retubing and then adjust after you retube. Try to carefully clean the tube pins to remove any grunge first. Do buy a few extra tubes incase some of the tubes blow, on or shortly after installation (a reputable dealer should be happy to replace them for you). Brent Jesse is one such reputable dealer, and there are others, Cary, I am sure would be happy to provide a replacement tube set as well. Tube rolling the smaller tubes and the 6SN7's is fun if your interested in doing that, but not a necessity. Access to a good tube tester is a nice thing to have,especially when buying tubes on-line. I hope this post gives you some helpful advise. Happy Listening,
thanks for all the details on tube u write me ,but i still dont know how much infulence have if i change the all tubes or the 4 power tubes and the 2 pre tubes in the sugesstion that give me see in the top of my first theards ?
and i wanna know if this kind of investment money on my cary amp tubes will worth it bcz this kind of amp is averge and nice and not so good like really good amp to my nines devore fidelity speakers (if i dont mistake) ??
and last thing what will be more good pre tubes to change in my cary : Amperex 7308 input tubes or EAT tubes ??
and where i can find it to buy anew and what the price can u send me link here to see and thinking ???
I've done a lot of tube rolling in various amps.The smaller signal,phase inverters etc.,seem to have some changes in transparency,less distortion,and some sonic characteristics.Changing the outputs had the most change in the amps sound characteristics.I can't speak for your amp,but in general the Chinese and JJ made outputs will be brighter and more detailed.The SED brand will have sort of a lush,and more liquidy characteristic.Its been to long to say what the KT88/6550 most modern tubes will sound like.In general what I'm trying to say is,the outputs will give you the most different sound between brands.For a different sound,maybe try the outputs first.
since you are new to tubes I suggest you do not change any tubes until you have listened to your gear many, many months, then consult the manufacturer and have them tell you what tube changes influence the sound the most and go from there. Do very gradual changes. Tubes are sensitive to unstable power from the wall and I'd suggest a device to lock in the current to 120 volts.
I believe Israel has 230 volts.Somebody from there may give an idea as to how their voltage and quality is in general.A lot of SS gear can vary with different utility
Shalom Bolero32: The small signal tubes(preamp, phase splitter and driver tubes) and your rectifier will make a MAJOR DIFFERENCE in the sound, imaging and sound staging of your system. That also depends on the rest of your equipment, cabling, listening room and speakers, and their combined ability to resolve these effects. McFarland has pretty well defined what you can expect from some of the better 6SN7s. The bottom gettered Sylvania 6SN7GT(40's-50's is a very clean and accurate tube, that presents a spacious sound stage, only bettered by their 6SN7W(tall bottle). Their are quite a few Amperex 7308s(various years, countries of origin, markings), that each has it's own sound(most are very nice). The EAT tubes compare favorably with the better NOS European tubes(Siemens/Telefunken), and are the best new production 6922/6DJ8 family tubes available now. If you can locate a pair of NOS Mullard 5U4G tubes, they will probably outlast you and the amp, plus surprise you with the differences they make in the sound of the amp. Enjoy your music and experimentation!
I'm with Larry,listen to your Cary with the stock tubes until you get a good idea of how they sound before you worry about changing them.