Folks, with all of this talk about re-tubing the SVP-Pro preamp, I thought I would post some information I got from Ampeg on the subject. I'm getting ready to embark on this same journey and I wanted to know the general layout about which tubes were doing what with the pre-amp. After a lot of searching and finding nothing, I figured why not try SLM. I should've done it sooner, they were very helpful! Anyway, here's the general overview the SLM service deparment gave me: o The tubes are numbered V1-V5 from left to right when the unit's control is facing you. Each tube is divided into two stages. o V1 is the Groove Tube 12AX7 when it leaves the factory and V4 is the 12AU7. o The signal enters the unit and immediately travels through stage one of V1, then through the gain pot and then stage two of V1. oThe bright, ultra high and ultra low switches are next up, then stage one of V2. o The drive pot is next up then stage two of V2 and stage one of V3, all of V4, the tone stack and finally V5. o "This is only a basic path of this thing? It's a bit complicated and actually has some parallel paths. If you are trying to really fine tune your sound be ready to spend a lot of time experimenting with tube combinations. Also, it is only fair to warn you that the SVP-PRO is very picky about the tubes you put in it; you'll have to search out nice, super-quiet tubes." (Directly from the SLM Service Department) I'm going to try some various combinations with 7025's (Ruby's I think), Sovtek 5751's, and possibly a Lord Valve recommended NOS 5814 in place of the 12AU7. My intention is to get the tubes early in January and then start the testing. I've layed out a test plan and hopefully I will have the discipline to follow it. I plan on recording a passage with the stock tubes both set to flat and to my preffered EQ setting. Then as I swap the tubes out, repeat the process again, each time recording to a new track. Even though I'll do my best to set the gains the same and play the piece the same way, I know it won't be a completly controlled experiment. Hopefully though, I will get be able to substantiate some of what I hear so when I'm on my 10th combination of tubes I can compare it to the others. If anything it will be a learning experience, but hopefully I can come up with even more tone!!!