Matched Tubes do I need them and why?

I have purchased a tube pre amp that has two 12aux7 and two 12 au7's for tubes. I would like to upgrade these an am wondering, do I need matched pairs of each? or do I just need to by new ones. I can get new for about 20 bucks, but have been quoted 110 for matched.

Please let me know what ya think and my apologies if this has been discussed before. Not much time to surf these days.
Thanks for your help.
It really depends on how they are used within the preamp, (for what purpose). I'm guessing (2) for the line stage and (2) for the phono stage? Then, yes they need to be matched. What make and model of preamp is it?
Depends on the actual circuit design of your preamp. Sharing the manufacturer and model of your pre will help others in answering your questions
Yes, you can get a decent pair for $20. Just buy from a reputable dealer:, and many more. used to match basic tubes for something like $1 extra.
Do you want the two channels of your system to sound the same or different?
Thanks for all the responses. The unit I am referring to is a P 307 Grant Fidelity In answer to your question I want the two channels to sound the same and correct. How do I ensure I am getting matched pairs. Are there specs on the boxes showing testing results are the same for each tube?

Again thanks for all your help.
You might consider purchasing them from Roger Modjeski at Music Reference.

He selected matched tubes for Atma-Sphere monoblocks I used to have in my system, and they never sounded so good.
Assumming that each of the tube types AX7 and AU7 are one per channel, then yes a matched pair of each is recommended. As to how to get them, if you are buying new, just ask the vendor to sell you matched pairs. They will charge more, but shouldn't be too much.
They should me matched. This should not cost much more. If you want to take your pre to a whole new level, buy NOS which cost more. I would guess the 12ax7 are for the phono, while the 12au7 are for the line. You can buy the most expensive pair for the one you use most.
Thanks for all your help, but how can I tell it is a matched set. Are the numbers on the side to be exactly the same? Some ratings on tubes show Idle and Dynamic db while others show T1,T2 and GM for each. If anyone knows of a web page I can get a good education in that would help. At any rate I am having some fun with tubes. Just bought a pair (hopefully matched) of RCA command's and gonna plug them in tonight.