It's heavy but I'll throw it out the window

[kingster911]

So I think I finally narrowed down this problem after having my amp in my trunk and never having taken it into Mesa. I was supposed to take it but just never got around to it after thinking i diagnosed the problem myself. got my RKII back inside today and it did the same thing: crackled like a mother fucker when I hit any hi-gain sounds in the slightest. The most cringe-inducing crackle noise ever. WHAT CAUSES THIS?

 

[Spewnz]

its probably a tube or a resistor issue. my roadster had a similar problem. just take it in.

 

[screamingdaisy]

Sounds like a power tube that's mechanically failed (ie, something's loose inside it).

Power the amp up with everything connected and turn your guitar's volume down to zero. Make sure your amp is turned up or else you won't hear if the test works.

With a short stick (pencil, pen, something like that) tap each of the power tubes. If one of them crackles when you tap it then it's pooched and needs replacement. Don't be afraid to tap the tubes firmly.

If that fails to turn up anything move onto the preamp tubes.

 

[kingster911]

For what it's worth: I replaced two of the 6L6's before and have the amp set on using just those. I will run the test soon like you said but in regArds to the 6L6's: do you have any idea which ones are in use while set on just two of them in the RKII? I'm suspecting you're right, and dreading that it's most likely the preamp tubes (those are the 12ax7s right?). Why does it only crackle hellishly on Ch 3 and 4?

 

[screamingdaisy]

For what it's worth: I replaced two of the 6L6's before and have the amp set on using just those. I will run the test soon like you said but in regArds to the 6L6's: do you have any idea which ones are in use while set on just two of them in the RKII? I'm suspecting you're right, and dreading that it's most likely the preamp tubes (those are the 12ax7s right?). Why does it only crackle hellishly on Ch 3 and 4?

If it's just 3 and 4 a preamp tube would make sense.

However, I've had it before where a power tube would only crackle when the amp is physically vibrated hard enough... which tends to happen a lot when doing high gain rhythm chugga chugga type stuff.

 

[kingster911]

Yeah I've hear that a little before but this is straight crackling through the speakers.

 

[Koreth]

If it is only happening on channels 3 and 4, I'd suspect a preamp tube. Per the tube-task chart in the manual for the Road King II, the preamp tubes that effect ch3&4 are V2 and V3. While V2 is shared between ch1&2 and ch3&4, remember that the preamp tubes used in our amps, 12AX7s, have two active elements in a single bottle. Ch1&2 gets half (V2a), and Ch3&4 gets the other half (V2b). The side that ch1&2 use could be just fine, but the side that ch&34 could be microphonic or unstable. Or it could be V3, as Ch3&4 gets both halves of that tube.

It is also entirely possible that the problem lies with one of the other tubes that effects the whole amp, like V1, V6 or the power tubes, but the problem is only revealed by the huge gain factor of ch3&4. But I would check V2 and V3 first.

 

[kingster911]

Took it in Tuesday and ran through it with Kris at Mesa. He ran through it testing all the tubes tapping on them and cranking the volume/switching tube combinations on my RKII. He swapped out ALL my tubes after finally realizing it was the EL34s...and those were all he charged me for! He said that they suffered microphonics? Someone explain?

 

[screamingdaisy]

Took it in Tuesday and ran through it with Kris at Mesa. He ran through it testing all the tubes tapping on them and cranking the volume/switching tube combinations on my RKII. He swapped out ALL my tubes after finally realizing it was the EL34s...and those were all he charged me for! He said that they suffered microphonics? Someone explain?

Something came loose inside it, so when it was vibrated hard enough whatever part was loose would clang around inside.