Peavey 5150....these were popular????

Matthews Guitars

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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.
 

Drinkingdeath01

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I just picked up a used old school block letter 5150 in a package deal and its quiet as a mouse. It doesn't blow me away but its still a great sounding amp. Has its own sound to it.

To me it blows away the Recto. Rectos sound flubby and loose, the 5150 is tighter and way more defined.
 

South Park

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You just can’t mass produce high gain amps and not get some noice in some of them . Every amp is different . Alway play them before buying
 

What?

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I used to gig a 5150 combo doing everything from clean to mean. Never had any abnormal noise issues with it. But I wasn't being a gain banger either. Played lots of rock, classic rock, and blues with it.
 

Ufoscorpion

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There is no problem if I can’t hear the hiss when playing as far as I’m concerned . If it a problem then put an ns-2 in the loop , sorted . You are going to get noise with high gain tube amps , it’s pretty much unavoidable .
 

Matthews Guitars

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Of course high gain is going to lead to higher noise levels. But this amp's noise level is absoutely epic. With no guitar plugged in, if you crank it, you can get noise complaints from your neighbor. And it's all due to what I simply have to describe as a pile of questionable design choices.

I bet that if I loaded the preamp with five blue tip Telefunken ECC83s, it'd STILL be noisy as hell just because that's what it's getting from thermal noise in the cheap resistors and received noise from the piss poor shielding.

I know these amps were very popular. I'm not sure exactly why. If they were this noisy when played on the guitar center floor, I'd expect players to decide to shop for a different amplifier as often as not.
 

South Park

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The contact points in the FX loop jacks can cause noice
 

80sTone

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I have the block-letter since it came out - no issues. It is a one-trick pony in my opinion and quite heavy to lug around, but has great lead channel. The clean is nothing to speak of, but then I did not get it for that anyway.
 

Rudy v

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I stil have some of the preamp tubes from the block letter i dont use them no more 15975073580823655006897166775105.jpg 15975074146812429840460804400900.jpg
 

vscrl1

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Am i the only one alarmed by the fact that the owner of the 2 amps the OP is talking about had the gain dimed and is using emg's? Ive owned probably 20 5150's and diming the gain is so completely unnecessary. No wonder the amps are making odd noises lol. Gain up past half is just dumb lol
 

Jethro Rocker

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Am i the only one alarmed by the fact that the owner of the 2 amps the OP is talking about had the gain dimed and is using emg's? Ive owned probably 20 5150's and diming the gain is so completely unnecessary. No wonder the amps are making odd noises lol. Gain up past half is just dumb lol
I missed that line! Gain dimed? Lead channel? Of course it is noisy as AF. Micropjonics will kick in at aome pojnt. Now, there may well be shortcuts internally that add ro the noise, it isn't a hand wired amp or such but no more noisy than other high gain amps. Mine is on perhaps 4 gain on Lead channel. The newer versions may have changed somethjng as well.
Also, it seems it doesn't make such noises when the fx in the loop are unplugged.
Gate in the loop amd go klll it!
 

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