Def Leppard is headlining one of the summer’s biggest tours — with Styx and Tesla in tow — but guitarist Phil Collen still found the time to steer an authentic blues side project dubbed Delta Deep, as well as put the finishing touches on Def Leppard’s new self-titled album coming out at the end of October. In addition to that, his autobiography, “Adrenalized: Life, Def Leppard, and Beyond” (Atria Books) is set to hit the shelves October 27.

While on a brief Def Lep tour break, Collen and two of his Delta Deep bandmates — lead vocalist Debbi Blackwell-Cook and drummer/percussionist Forrest Robinson — stopped by to perform two songs from their self-titled album, and Collen sat down to discuss the origins of Delta Deep, why Def Leppard continues to endure, and his über-healthy lifestyle.

FOX411: How did you first get into the blues? It seems like it’s in your DNA.

Phil Collen: I grew up listening to blues-based rock, so I got the second-hand or third version. It first came from slavery and the blues, and then we had Delta blues, and then it became electrified Chicago blues. I learned Led Zeppelin, Deep Purple, The [Rolling] Stones — that was all blues-based kind of rock music. That’s where it all came from. People like Jimmy Page and Jimi Hendrix were playing the blues, although it was plugged in and very loud. That’s how I got attracted to it. That’s really how I found out about the blues.

And I got my first guitar on my sixteenth birthday. I asked my mom and dad for one for about two years, and then I got a Gibson — which was a huge deal to buy, because my dad was a truck driver.

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FOX411: When you were growing up in the ’70s, you got a record called “The Guitar Album,” and there were some pretty famous blues artists on it.

Collen: Yeah. This album had B.B. King doing “Sweet Sixteen.” And it was my birthday, so it was really profound and poignant, the fact that I got this guitar and this album that had such great playing on it. It had Hendrix, Duane Allman, Roy Buchanan — all the guys, all the blues players.

FOX411: You got to meet B.B. King last year, right?

Collen: I did get to meet him briefly, yeah, on my 56th birthday [December 8, 2014]. I told him I had been playing guitar 40 years to the day, and I had gotten this album with “Sweet Sixteen” on my sixteenth birthday. So he sang “Happy Birthday” to me, which was pretty cool.

FOX411: That is pretty sweet. How did the band Delta Deep get together?

Collen: A quick recap! Debbi Blackwell-Cook, the singer — who’s also my wife Helen’s godmother — has been singing in the church since she was two years old, and she also sang at our wedding. Whenever she was around the house, she’d be playing Motown songs or kicking blues things. We performed acoustically at a charity thing at the Gerson Institute [for alternative, non-toxic cancer therapy] in San Diego, and everyone kept going, “Guys, what is this? Where can we buy this?” It was just us playing around and goofing off!

So we started writing songs, and then it took on a different form. We got Robert DeLeo from Stone Temple Pilots on bass and Forrest Robinson on drums, and that’s when it started sounding different from what we had imagined it to be. We thought it was going to be this rootsy, bluesy, Motown-y kind of thing — which it is — but it also sounds like Rage Against the Machine when we get all fired up. When Forrest started playing almost heavy metal drums on it, that’s when it took on this thing where it was more Led Zeppelin than Muddy Waters.

FOX411: New millennial blues, we could call it.

Collen: Absolutely, yeah! I think it’s still retained all of those elements — all of the funk, the soul, and the blues. They’re all combined anyway, and I think the great thing is there’s a sense of liberation about it. It’s free. It doesn’t have to be confined to just the blues genre or anything like that. It’s all of the above. It’s really inspiring.

FOX411: You mentioned the name of that other band you play with — what was it called again, Ded Flatbird…?

Collen: Ded Flatbird, yeah! [Ded Flatbird is actually the name Def Leppard used when opening for itself during the band’s “Viva Hysteria” run at The Joint in Las Vegas in 2013.] Now we’re on the ongoing Def Leppard tour. We’re experiencing a real boost in our career at the moment, for whatever reason. We started a world tour last April in Canada, and we just keep adding legs to it. It goes way into next year. It will probably end at the end of 2016, the way things are going.

FOX411: I’ve been out on the road with you all over the country on this tour. Last week in the Midwest, just for the last three shows alone, you had crowds of 16,000, 17,000, and 18,000. I asked your drummer Rick Allen about why it seems to be getting bigger and bigger for you, and he told me how he has an 18-year-old daughter who used to listen to all kinds of music, but now she’s really into classic rock. What do you think the reason is for all these fans coming out to see you?

Collen: A lot of things. There’s a clear divide in the days where you can just stream music and when you could actively buy and really seek the stuff out, if you’re really into it. You don’t want to listen to what you’re being told on the radio or all those TV shows. There are these great records out there — everything from Miles Davis, The Beatles, The Stones, Led Zeppelin, and us included in that bunch. I think people are actively searching that out.

And it’s also the fact that we actually still exist. We’re a real band that tours. We’ve got a new album coming out at the end of October, so it makes us a lot more real. And then when you see us live, we actually sing — it’s not samplers or tapes, or any of that stuff. It sounds different, just like Delta Deep does — when you hear us singing and playing live, it’sreal. That’s a huge thing for people. They’ll go, “Do I want this pre-recorded, unreal version, or do I want the real live thing?” So they’re getting that as well. I think there are a lot of elements to it.

And the fact that there’s the “last man standing” thing with Def Leppard. A lot of bands who were our contemporaries in England have fallen off, and just stopped — but we’re thriving and flourishing. That’s kept us going.

FOX411: You live an extraordinarily healthy lifestyle now — you’re a vegan, and you haven’t had a drink in 25 years. In the old days, you used to drink to the point of going naked into restaurants. Tell me about the change from being known as a Terror Twin to the person you are today.

Collen: Well, I still go into restaurants naked, but I just do it sober now. (both laugh) As I get older and more experienced, I find I don’t want to be like some of my friends. I go back to England, and I see people 20 years younger than me who can barely walk, and they’re hobbling around. A lot of it comes down to diet. You don’t have to do crazy exercise, but you have to be somewhat active. We get less and less active and more lazy as we get older.

The reason I don’t eat flesh is for moral reasons. It makes a difference. And I found that the health benefits are amazing. I do know some unhealthy vegans, but I’m not one of them. (chuckles)

FOX411: The subtitle of your book “Adrenalized” is “Life, Def Leppard, and Beyond.” What does the “Beyond” part mean for you right now?

Collen: Delta Deep is part of the “Beyond.” I’m not defined by just being in Def Leppard. It has been an amazing way to discover stuff — I’ve traveled around the world and met some really interesting people, and I know more every day than I did the day before. That’s an amazing thing. But I’m still a work in progress.

Delta Deep plays Players in New York City on Friday, September 11 at 8pm. For more on that gig and the band, go to DeltaDeep.net. For the latest on that other band, go to DefLeppard.com.

Mike Mettler is the former editor-in-chief and current music editor of Sound & Vision, and he interviews artists and producers about their love of music and high-resolution audio on his own site, Soundbard.com.