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 :-}
bolero32
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.
Larry
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
fluctuations.
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.