I was asked to try to figure out a problem a local player is having with both his Peavey 5150s. (First version.) OK, fine, I'll take a look. Never have had a chance to screw around with a 5150 before, so if nothing else I'll get to play. I suspected from the start that since he's having the same problem with two identical amps, a problem that doesn't appear to be common, then it's probably not the amp. Well...that's correct. He was reporting that the amp would start whistling after it's been on for a while. I asked him to tell me his settings. Lead channel, master at 3, gain maxed. Guitar, active EMGs. Moderately complex pedal board plugged into the front panel input, except for a noise gate, which is in the loop. Yeah, I see where this is going. Funny enough, the problem doesn't happen when he plugs direct into the front of the amp. It's just too much system gain causing oscillations. Nothing wrong with the amp. Except... Man, are these things noisy or what? Truly I've never heard an amp that has so much noise to it. It bugged me enough that I took the chassis out of the cabinet for inspection. I'll deal with the construction later. First...let's check those tubes to see how noisy they are. I have a means of testing tubes for gain and noise and it's by plugging them into V1 of my Mesa Dual Recto in the green channel, pushed mode, every channel control dimed. Volume controlled with the output knob. But before checking the 5150's preamp tubes, I pulled out five previously selected tubes that have good gain and very low noise to swap into the 5150 for test. Which I did. And it didn't seem to change the noise level very much. Yeah, the amp itself sounds like a hailstorm on a tin barn roof. Seems to be the nature of the beast. I checked the 5150's preamp tubes and found that apparently they could all be ORIGINAL, but only one actually was bad. It's worn to the point that its bias point has shifted and it gates like mad. You can do synthesizer buzzes and vary the pitch by rolling your guitar volume control around. When the tube's bias point has shifted like that, it's toast for sure. At a high gain/guitar volume setting, it squeals like a pig with a cow shoved up its butt. So I swapped that tube out for a better one and put the set back in the amp. Now about the construction....was Peavey TRYING to make an amp with as many noise problems as possible, or was that just a happy accident? Preamp board located in its own little compartment with the tubes turned sideways, to allow tube changes from the back of the amp without having to pull the rear grille. BUT... the grille removes with four screws. The preamp compartment cover is held in with six. Not seeing the convenience. Most of the components are 1/4 watt. Not good practice for tube amps. They appear to be noisy carbon film resistors. An extra penny or two spent per resistor to upgrade to metal film would yield significant benefits to the noise level of the amp. And...larger wattage resistors are less noisy. A few more cents per resistor to upgrade to 1/2 watt metal films would not have increased the build cost per amp by more than a few dollars! The preamp board is connected via a few ribbon cables with push-on connectors over PC board mounted pins. None are even gold plated. This is not a reliability plus, and since none of the cables are shielded, there's part of your noise. The chassis is open topped without a shield, not even a metal foil sheet inside the head cabinet. That's certainly another reason the amp is noisy. The head cabinet is built a bit too small. There's little room for error or adjustment when installing or removing the chassis. It's almost a requirement that you remove the two metal corner protectors from the lower rear of the head cabinet before you can easily remove the chassis. If you can deal with the absurdly noisy character of this amp, the tone is quite good. I do like its sound but at that noise level I honestly don't know why anybody who plans to use it at stage volume would buy it. Or at least they'd better get a good noise gate and put that in the loop. The amp's sound is good aside from the ridiculous noise level from it, and as for construction, it was made to be built fast, not serviced easily. Even the main filter capacitors (some of them) can't be replaced without pulling the outpt PC board up out of the chassis. This amp actually uses filter capacitors that are soldered to the main PC board. Radial lead, no less. (Some of them.) I have nothing positive to say about that design choice. Tonally speaking, it doesn't do anything that my dual recto doesn't do as well or better, and do it with a much lower noise floor to boot. My advice: Get a dual or triple recto instead. It's just a better amp.