KT_88 : Just my gut feeling but if you can find a good "new " quality stock tube that works well with your unit, stick with it.You can save money buy buying cheaper stock tubes and get who knows what, or buy from a person or comapny that test and screens tubes and matches,which cost a bit more but sound great and last.To me the new tubes of today are getting better.There are good deals on NOS,but hard to find and you need to do your homework. Good Luck