Matched Tubes do I need them and why?

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: Upscaleaudio.com, echohifi.com and many more. tubesandmore.com 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 http://grantfidelity.com/site/P307. 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.

Cheers,