Would you buy a tube amp if you were unable to use vintage tubes in it ?

If you bought it new with new tubes, you liked it with new tubes; if it turns out it sounds even better with old tubes, that is just a bonus.  Most of the time, I prefer carefully selected vintage tubes.  But, it can be quite a process auditioning various types and brands.  For the gear I own, my linestage and amp have very limited modern options; if I stick with the correct tube type—348, 349, 310–it is primarily Western Electric and scary expensive (so far, I haven’t had to replace a tube in about 15 years of operation.

Fifteen years for the amp and linestage and the tubes that were put in those two components were old to begin with--they tested good, but prior usage was unknown.  Both components run the tubes very gently.

I also run tubes in a headphone amp and a phono stage.  I would have also recorded no tube failures in these two components as well, except a shelf collapsed onto the power supply of the phono stage and wrecked both rectifiers.  This is a very odd phono stage-Viva Fono- that utilizes two 300B tubes as rectifiers.  So, this was not a cheap replacement caused by that shelf failure.

I would have some doubts about any such extreme longevity unless the tubes are run VERY gently.  There are some people who claim their table radio has been left on constantly for decades so it might be true that some tubes can last for a very long time.  The particular Western Electric tubes I run have lasted very long for me as well as for a number of other people who have bought similar gear made by Aldo D'Urso, an Italian builder who is very much into Western Electric gear.  

The 40,000 hour figure comes from original WesternElectric 300B operations and does not necessarily apply to all 300Bs.  Some, such as Elrogs were notorious for quick deaths.  As for the new reissues, it is to early to tell, but at least they have a long five year guarantee.  Another issue is that some modern amps really push tubes very hard to be able to claim high output power.  I would personally prefer an amp that runs the amp very conservatively.  Another issue is that a lot of American power grids deliver power at 120 volts or more and this can be hard on tubes.  I know tube people that employ step down transformers, one to as low as 100 volts.

I don’t think you need to go so low, 115 volts would be within any specified operating voltage and it would be significantly gentler on tubes.  Too low and performance may suffer and might actually be a problem if your amp has voltage regulators.  The person I know who set voltage at 100, knows what he is doing and can adjust other operating parameters of his gear.  Some amps do run small signal tubes hard too, but that is not usually a big concern.  There are some who don’t use these tubes as drivers for the 300B because they may not have enough grunt (or may be pushed a little hard to deliver sufficient output), but many amps do use these tubes as drivers.  The subject is complicated, as some amps use interstage transformers which reduce the need for grunt from the driver.  Hence, it is hard to generalize.

If you can't hear the difference between say an Amperex Bugle Boy 12AX& and a vintage Telefunken ECC803s and current manufacture tubes, either there is something wrong with your gear, or your ears, or both.  I don't go crazy with tube rolling myself, but I do hear substantial differences.  So much of what is right is a matter of matching a system and personal taste.  The only 12AX7, or similar tube type, that I run in my system are the vintage ECC803s tubes in my phono stage.  A good friend of mine cannot stand that, or any other Telefunken tube.  Tastes do differ.

Inna, 

You have a steady 120 volts and that should be good because gear is made for that voltage.  In some parts of the country, one can see much higher voltage, such as 125-127.  That high a voltage would be of concern for some, but not all tube gear and it makes sense to back that voltage down.  If one can back it down it might make sense to go to the lower end of the acceptable range of voltages such as 110 volts.  My voltage is fairly steady at 117 volts, although it does rise to 120 volts once in a while.