What would cause this noise?

[trey85stang]

Here is a 30 second clip of my mark 3. There is no guitar hooked up.. so this is just the amp by itself through a speaker.

http://trey85stang.googlepages.com/mbm3noise.mp3

There is a hum, which I dont care about but there is also a crackling sound that is presnet that is annoying me greatly... Im thinking filter caps but im not sure and would rather be sure before I go replacing them? Bad tube perhaps? Its not powertubes as Ive tried new ones as well as some older ones I have laying around they all do it. It could be preamp tubes as ive only put in old ones no new ones yet but everyone I have seems to do it.

Any ideas?

[stratman_el84]

Hard to be sure, but it sounds like 'aged carbon-comp resistor syndrome'. Carbon-comp resistors tend to get noisy when they get too old, and typically produce crackling/popping noises as they warm up.

If you're experienced electronically and know how to be safe working in circuits with high voltage, remove the chassis and fire up the amp. When the noise starts, try using a 'chopstick' to tap on preamp tube plate resistors and/or use a bit of 'cold spray' on each resistor in turn to see if that's the culprit. If you're not knowledgeable and/or confident in your ability to work safely with hazardous voltages, take it to a tech.

Cheers!

Strat

[Structo]

Tubes are always the first suspect.

How old is the amp?

I am not getting anything on your link and MP3 file.
It just opens a page with nothing on it.

But from your description I would suspect a preamp tube first.

[Norse]

I've found this noise caused by a few different conditions:

1. loose tube sockets.
2. loose speaker jack nut.
3. loose input jack ground contacts (the inputs you're not plugged into).

Of course there are many other things that can cause this noise, but these are what I've found so far. The advise given earlier is good and is how I found the problems (poking around with a chop-stick). The resistors mounted on the output tube sockets is where I would look after scrutinizing the tubes themselves (substitute or tap them lightly - feel the socket tension with a chopstick).

Be careful in there with the high voltages - if you're not familiar with this aspect - do that first!

Good luck!
Greg

[trey85stang]

im familiar with high voltages.. I did some checking and checking and more checking based off the good stuff in here but I am not getting anywhere. I do however have a few resistors that need to changed and will report back after I swap those. (except for the above mentioned input jack.. I need to check those).

I guess I need to get some fresh preamp tubes to try. btw, the amp is a mark3 it was made in 89.

[trey85stang]

Originally Posted by Structo

Tubes are always the first suspect.

How old is the amp?

I am not getting anything on your link and MP3 file.
It just opens a page with nothing on it.

But from your description I would suspect a preamp tube first.

right-click save as should let you download it.

[Blue Strat]

Have you swapped in known good preamp tubes? That's your first step and doing anything else before this is a waste of time.

[trey85stang]

Originally Posted by Blue Strat

Have you swapped in known good preamp tubes? That's your first step and doing anything else before this is a waste of time.

All the tubes I have work fine in other amps with no noise.

[donnyjaguar]

It sounds like a shagged plate resistor to me. Discharge the amplifier and measure the resistance of all the plate resistors comparing them to their values. I bet you find one that's a lot higher than its supposed to be.