I play a '75 Gibson Les Paul Deluxe, which has been modded to be closer to a Standard model, with a Gibson '57 Classic humbucker in the bridge and a Seymour Duncan JB (I believe) in the neck. The bridge pickup and this amp equals an almost unrivaled rock sound, with the volume set anywhere above 10:00. Huge, full, every note in a chord shines through. Notes sustain forever and dissolve into controlled feedback. At about 10:00 on the volume, think AC/DC, Hellacopters, Stooges and you'll get an idea of the sound. Above that, it gets into even heavier territory. I've played vintage Marshalls, and I will vouch that this amp blows them away. The neck pickup with this amp yields a slightly cleaner sound. Sounds best with the volume at about 9:00, with a little of the amp's spring reverb added in (thank god for the footswitch). It's pretty reminiscent of the tone on the Wipers' "Over the Edge" album, or the guitar sound on Hot Snakes' records. Shimmering like a Fender, but with a hint of dirt.
The amp was pretty noisy when I first got it. But a new grounded plug fixed all of that.
I just got it back from the shop. I anticipated a tech visit in my near future when I bought the amp, being that the whole thing was pretty much stock. When I first got it home, I played with it a little, cranked it up and whatnot. It sounded great. Then I started playing around with the knob that had been added on the back of the amp, blindly assuming it was an aftermarket master volume knob. Hey great, now I can get distortion at reasonable volume. Well, whatr didn't occur to me was that, in addition to master volumes being added to these old Ampegs, lots of people who originally owned these amps were having bias adjustment pots added to them as well. Not even considering this, I cranked the "master" knob to full, attempting to bypass it. Within five minutes, the power tubes were redplating and flashing. My amp tech removed the pot altogether, installed the three-prong plug, replaced three preamp tubes, and gave it a clean bill of health. Got it back home last night and cranked it up again. Sounds awesome. I think this is a very reliable amp, with regular basic maintenance (changing tubes when needed, cap job, etc.). In fact, I will probably have a complete cap job done to this one very soon, to ensure it remains in working order.
I'm admittedly a big fan and champion of the early 70's Ampegs. I own this amp, plus an early V-4B, a blueline model B-15N (the best amp ever made for recording bass, seriously), and I co-own an early model VT-22 with a bandmate, not to mention an early 80's MTI-era SVT. I also own a vintage Traynor YBA-1 that I use for guitar. The VT-40 is a top of the line amp. Sounds on par with my V-4B for guitar (and it is one of the best sounding amps for guitar that I've ever heard), and is easier to carry around in my car. If it was stolen and I had the cash, I'd definitely look for another. Has everything I need and nothing more, just the way I like it.