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Major snippage below to keep post length down. [/qb] John, The phase inverters, as there are two of them in an SVT, are important to be matched. The line outs are used to slave additional power amps if the need ever arose (which is pretty humorous as the SVT family, old or new, are pretty extreme amps just standing alone. I mean, they were big enough to do the original Woodstock without the help of sound reinforcement A balanced phase inverter will not give you a change in level or tone. What it will do is give you sustain across the entire fret board, especially on bass and its lower frequencies that really tax amps. So .... in comes GT SAG folks. Now you plug in a tube that is a #100. Down the road you want more compression and less front end distortion, so you order a #80 or so. Or ... you want LOTS of gain, so you go for a #125 maybe. V1 and V2 are your basic tone shaping tubes, others are used for the tone controls and EQ. Your most important tubes are V1 and your two phase inverters. Regards,[/QB] Thanks again Myles. I wanted to know specificaly about the newer SV P, the preamp only unit from SLM. Does the 12AU7 tube drive the line outs? Even more specificly, does each side of the 12AU7 amplify half the waveform (push-pull style as in a normal SV T ), thus needing a balanced tube, or is there a difference between the stand- alone preamp (SVP) and say the integrated pre in the SVT 2 Pro or SVT 4 Pro heads? Hope I'm making sense...

John, O.K.... here we go ... Your AU7 could be a GE, RCA, or Philips. I'd have to look at the tube to tell, but they are all good ones. You are correct, V1 is the closest to the input jack. The others are for various gain stages for the most part with V2 also doing tone control duties. For what you are looking for, in V1 and V2 you have a few options. One option to brighten things up is to try a 7025 in V1. For more compression, you want V1 to have a longer rise time, and for this you need to find somebody that can find you a tube that was looked at on some pretty sophisticated equipment. Most folks only look at emissions, and that measurement is not the same as rise time. The only folks I know that do this are Groove Tubes, and thats for some of their select clients. I'd use a GT-12AX7R in that position, but have it picked for a MS (medium slow) rise time with a rating of 108 or higher. The rating of "108" is a rating I use for my clients, but some of the folks at GT know my rating system. They have a group over there called SAG or Special Applications Group, that might be able to get you that tube. You'd have to call them direct as I don't think those are dealer stocked items at all. I have blueprinted a number of SVT's. There are a lot of factors involved with them, as there are 6550 versions and 6146 versions. It also depends a LOT of the player's style, and 4,5,6 string instruments, and even the string guage comes into play. If you talk to GT, the guy to talk to is Rick Benson. He's the head of their sales department, but very technical, and maybe the only one that knows of their SAG (sort of GT's Skunkworks). He may not admit much, as like the Skunkworks, is sort of kept under wraps. Hope this helped. Regards, Sorry for the last post with no new text- I must have hit "Add Reply" too soon This is what I meant to post: Thanks Myles. As allways, good info. (By the way, I read the whole "ask Myles" thread over the course of a couple of days. What an education!) Now for the next question(s): If this was the pre- of an SVT, then I would assume that the 12AU7 was a phase inverter/ driver and having a ballanced tube would be important. The SVP has line outs, and I would guess they are driven a little differently... do I need a ballanced tube here to give a strong, pure output? I tried a US made GT 12AT7 -not sold as ballanced- without much change in tone, or seemingly, output. Next... Something I could try if GT doesnt't think a guy who mainly plays bass for his own ammusement is worthy of specially tested "skunkworks" tubes, is to order a mess of ECC83/12AX7 tubes from Eurotubes and just listed till I find the tone I'm after. I liked the sound of the Mesa SPAX7 in there too, so I could try a few more of those, but the JJs are almost 1/3 the price and have the same odds of finding one I really like. So V1 and V2 are the main tone shapers? What about the tube on the other end (Right side, viewed from the front)of the daughter card? Whatever it does, it seems to respond to the Mesa/Boogie nicely... John P.S. If GT told me about the SAG, would they then have to kill me?

John, O.K.... here we go ... Your AU7 could be a GE, RCA, or Philips. I'd have to look at the tube to tell, but they are all good ones. You are correct, V1 is the closest to the input jack. The others are for various gain stages for the most part with V2 also doing tone control duties. For what you are looking for, in V1 and V2 you have a few options. One option to brighten things up is to try a 7025 in V1. For more compression, you want V1 to have a longer rise time, and for this you need to find somebody that can find you a tube that was looked at on some pretty sophisticated equipment. Most folks only look at emissions, and that measurement is not the same as rise time. The only folks I know that do this are Groove Tubes, and thats for some of their select clients. I'd use a GT-12AX7R in that position, but have it picked for a MS (medium slow) rise time with a rating of 108 or higher. The rating of "108" is a rating I use for my clients, but some of the folks at GT know my rating system. They have a group over there called SAG or Special Applications Group, that might be able to get you that tube. You'd have to call them direct as I don't think those are dealer stocked items at all. I have blueprinted a number of SVT's. There are a lot of factors involved with them, as there are 6550 versions and 6146 versions. It also depends a LOT of the player's style, and 4,5,6 string instruments, and even the string guage comes into play. If you talk to GT, the guy to talk to is Rick Benson. He's the head of their sales department, but very technical, and maybe the only one that knows of their SAG (sort of GT's Skunkworks). He may not admit much, as like the Skunkworks, is sort of kept under wraps. Hope this helped. Regards,

Myles- What an awesome amount of information here! Thank you! Now for my question(s): I have a SVP bass pre-amp that came with 4 old type Sovtek 12AX7 tubes and 1 US made 12AU7 (GE?) The tubes are all mounted on a daughter card from L-R AX-AX-AX-AU-AX. The input jack is closest to the left so I think V1 is on the left? Can you tell me if my guess is right, and what the other tubes are for? I would like to end up with a compressed, punchy but bright clean tone (just on the edge of audible distortion) that will turn to a nasty punchy distorted growl (Rush on steroids but with full bass), when I crank the drive control to 3 o'clock and beyond. Right now I have a mix of tubes in there: a Mesa/Boogie SPAX7, a JJ "high gain" ECC83 from Eurotubes and a GT 12AX7R-2 in ther, all left overs in a tube tone quest in my guitar pre, an ART SGX 2000 Express. (The winner in *that* quest was another JJ ECC83) Have you worked with blueprinting any SVPs (or SVTs, as they use similar pre-amps)? I would really like to get this sounding better for bass than my guitar pre-amp does (since I found the right JJ for the SGX from Eurotubes). Thanks! John York