I have a brand new amp (beefed up 5E3 style) perfectly tuned with a pair of NOS 5881 tubes. Now I'd like to break in the speaker with an Ipod or other similar methods that don't require any quality in tone, so my idea is to put in a cheap used pair of 6L6's for the process. My question is whether doing this will alter in any way the bias or other parameters in the amp. I'm asking because of course when the break in period has ended I want to put those NOS 5881's in there and have everything perfectly tuned-up just like now. Thanks for the help!