Preamp Valves - matched?

[Tricalibur]

So I own two vintage Mullard 12AX7's which I believe are a matched set. I want to put them into my Matamp head but I need to buy one more to complete the preamp stage. Do preamp tubes need to be a matched set to sound the best, and do I have to drain the voltage out of the amp before I remove the old tubes?

[martinw]

No, and No. Just turn the amp off.

[AdamB]

Only the power amp valves you need to have matched to get the best out of them. Pre amp valves, you can mix and match, low gain, high gain, whatever you like :D

[JamesHealey]

yea pre-amp tubes are cathode biased which means it doesn't matter you can just about drop anything in there and it'll work, yet ideally in a perfect world u'd change the anode resistor and cathode resistor for new types of pre-amp tube like 12AU7 to get the perfect bias.. but who the hell does that?

Just plug and play my friend.

[the_bleeding]

since preamp tubes amplify by cascading each stage sequentially, matched bias doesnt matter.

Matched bias only matters in the output section of Push/pull amps, because it splits your signal in 2, and amplifies the negative and positive sides seperately, and you want those sides amplified equally.