#1
Hey, guys. I own a 6505+ 112 combo amp and I just recently noticed crackling when I get the post gain up to about 4. I tried two different cords, two different guitars, and two different outlets on different circuts. Would this maybe be a tube going out? It seems strange to me because the amp itself is only about 5 months old give or take a month. I bought it from musiciansfriend.com and got it from UPS around April of this year. Currently, I have had it at around 4 or 5 at the maximum volume and I don't do it that often. Once a day more recently, but I used to rarely get it above 2. So, what could be doing this?
#2
The crackling sound you hear could be the result of an arcing tube. Tubes are funny animals. Even if you buy a new amp, a tube can go out a couple of weeks later. I've experienced that on a Mesa amp and had a bad crackling noise on a Rivera amp.

Try making the room dark and spin the amp around, so you can look into the back. Crank up the gain to the point where it begins making the noise, then watch the tubes. You're watching for one of them to exhibit arcing. You may or may not see it. If not, you'll have to use troubleshooting skills to isolate it.

Does it happen on both channels?
Does it only happen when the reverb is turned up?
Does it only happen when ???

These are all clues as to which tube is causing the problem. The tubes in your preamp can usually be swapped. Be sure to mark them for their original location, since manufacturers will sometimes use different versions of the same tube type in different sockets for different characteristics. Turn the amp, allow the tubes to cool for a couple of minutes, prior to removing them. Once you isolate it to a certain tube, mark it as "arcing", reinstall it and order a replacement, unless you already have one on-hand.
#4
Quote by UntoExistence
is it a occasional crackling, or more like a continuous hum? when my 6505+ head is past 4 it's pretty noisy

It's crackling. I hear a slight hum, but this is literally little pops and cracks.

EDIT: Also, if it is a tube, could someone help me out with biasing? I've never done it and I'm pretty sure this amp requires biasing to get the best life/tone out of the tubes. Any help here?
#5
If it does require biasing and you've replaced the power tubes, you'll need a special socket that plugs into the amp's chassis, and then the tube plugs into it. Some amps may have a special test point. Either way, you'll need a digital voltmeter. There's also the concern of touching something you shouldn't inside the amp and getting shocked/injured/killed. If you don't know what you're doing, it's probably best to have someone show you the first time, or take it to a guitar store and have them do it for you.
#6
Quote by KG6_Steven
If it does require biasing and you've replaced the power tubes, .

the 6505 series didnt need biasing. As far as I am concerned, they only need a matched set of tubes you cant bias them
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#7
I've got a good feeling thats its just a preamp tube which don't need biasing. This happened to me a while back, crackling and popping. Swap out preamp tubes until you find it.
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#8
Quote by JoePerry4life
I've got a good feeling thats its just a preamp tube which don't need biasing. This happened to me a while back, crackling and popping. Swap out preamp tubes until you find it.

Well, I know the pre amp tubes don't need biasing. What I should've asked was; Should I need to replace the power tubes, how do I bias them/Do I need to bias them. Since I don't need to bias them according to one of the replies, I don't really need an answer to that question.

Oh, and by the way, there isn't anyone around here that knows how to bias nor is there a guitar store that will do it for me. That's why I asked you guys.