Scratchy noises sometimes coming from my Mark III

[Skyless7620]

I was jamming on my new Mk III earlier and then the signal started cutting out and/or becoming scratchy. I go in the Back and check for a bad tube, they all look fine, except one of the 6L6's in the outer position was a lot hotter in temperature then the other ones (the Mesa Engineering logo on the tube has dissapeared by some black/chrome looking color, but I've seen those before... its normal right?) Anyway... I turned off the amp for about 5 minutes to examine it... turned it back on for about 2 minutes... closed it again and checked the temperature... said tube was still way hotter then the others. Sound like a defective tube? I hope it is...

 

[stokes]

Could be that the tubes current draw has drifted so it is running hotter than the others.The crackling could be the tube starting to arc internally,could be about to fail.

 

[Skyless7620]

I'm thinking of playing it safe and just buying a pair of 6L6GC's tomorrow and just replacing it. My Mark III is rackmount and I just noticed that I had placed the fan wrong in the sense that air was going out and not going in so the amp had no cooling also :S. Could this be a cause?

 

[stokes]

Even with the fan drawing out it will still offer more cooloing effect than no fan at all,many amps have no fan.I dont think this would be the cause.Besides,if it were the problem,all the tubes would be getting overheated,not just one.Remember to change tubes in pairs or quads,dont try to replace just the tube that is overheating.

 

[Skyless7620]

so if the troubled tube is an outside one then I should replace the two outer tubes correct?

 

[Skyless7620]

I opened it up again a few minutes ago and thistimeit was completely dead. Nothing more then a Hum in Lead mode and completely silent in both R1 an R2. I plugged the guitar in the effects return to check for sound and there it was. So, I guess that adds a V1 and V2 12AX7 on the "to buy" list... ****

 

[stokes]

When you say you "plugged in to the effects return to check for sound and there it was".What do you mean "there it was"?Are you getting sound or not? If you get sound when plugged into the return,it could be a problem with the send jack,you can check this by bridging the send and return jack with a guitar cable.If the amp works properly with the jacks bridged,you need a new shorting jack foor the send.This problem would not be related to the earlier "overheating"tube issue.

 

[Boogiebabies]

In the combo's the far left tube is always hotter because it does not get the same airflow from the fan. the scratchiness is usually a dirty volume 1, or it has a dead spot. The same could be said for the preamp tubes. Sometimes all you have to do to test them while noisy is turn the stanby off for a few seconds, then turn it back on. So try turning your volume 1 in lead mode and then try swapping the pre's 1 at a time.

 

[creative]

in my old marshall i haved this problem for months and it was ground wire. little soldering solved my problem.

 

[lpstudio]

I had the same problem with my .50 cal and it was a bad preamp tube

 

[Skyless7620]

I just got the new tubes just in case, I will try what people here have mentioned. I fired it up a bit to see if it had changed a few minutes ago and low and behold it was working wtf. poweramp tubes got pretty hot pretty quickly but they all appear to be working. I'm gonna play a bit and if symptoms appear again I will swap V1. Sound like a plan? I have two new 6L6's also but I wouldn't want to use them if I don't have to.

 

[Skyless7620]

I Originally had 430's in both inner and outer tube pairs in the power section. I now have yellow 440's in the outer sockets and a new V1 12AX7. Sounds good. Someone tell me now if I did something I shouldn't be doing LOL.

 

[Boogiebabies]

I Originally had 430's in both inner and outer tube pairs in the power section. I now have yellow 440's in the outer sockets and a new V1 12AX7. Sounds good. Someone tell me now if I did something I shouldn't be doing LOL.

It's probably paranoia. :shock: