#1
Hey all, what's up. First time posting in here. I've been a proud owner of a Mark V head for a little over 6 months now and been having a blast, for the last month though each time I open up the amp, I hear crackling noise coming from the cab. I've done a bit of research and came to the conclusion that it's probably due to a tube failure.

Now, here's my problem, I'm horrible at doing tech stuff, and I'm really nervous of playing back there and removing tubes and stuff. It's most likely a Pre-Amp tube problem, but those ones are behind the power tubes and I can't see my self reaching them, do I need to remove all the Power tubes in order to be able to remove Pre-Amps?
How do I make sure it's a tube problem instead of say, a cable? Are there any good videos out there that show you how to do it properly?

hopefully, other Mark V owners will know what I'm talking about...Any help is appreciated, Thanks All!
#2
Crackling can often be indicative of an overly microphonic preamp tube - but, to your point, it could be something else.

I'm not familiar with the Mark V at all and I'm not an amp tech but here is a little vid I did that might help you troubleshoot. With some amps you have to slide the chassis out by unscrewing it from the headshell. As long as you don't touch anything on the inside you'll be fine. Maybe someone with a Mark can weigh in.

http://s545.photobucket.com/albums/hh384/buckethead_311/Amp%20stuff/?action=view&current=Microphonicpreamptube.mp4
#3
Is it when you turn a knob?

What exactly do you mean by "opening up"? Volume? Literally taking the back of the amp off?
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#4
By opening up, I mean switching the amp on, it also distorts a bit everything I play, like on the clean channel you hear a buzzing each time you hit a note.
#5
Quote by Zonzin
By opening up, I mean switching the amp on, it also distorts a bit everything I play, like on the clean channel you hear a buzzing each time you hit a note.

Tube rattle maybe?

Take a pencil, with the amp on, and tap each preamp and power tube gently with the eraser. if the tap comes through (as in very prominently) then that's the bad tube. Power tubes going microphonic is rare.

I had a head that crackled a little whenever I switched standby off. Never did anything past that; just crackled then, and then operated normally.

The sound while you're playing makes it sound like a microphonic tube.
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#6
Are you sure it's not the cab?

Sounds like a blown speaker to me...


Could also be:

Microphonic preamp tube
Dying power tube
Bad speaker cable
Bad instrument cable
Faulty pickup wiring
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Last edited by MatrixClaw at Mar 29, 2011,
#7
Thanks for all the responses all, is there any way to figure out if it's a blown Speaker? to check the Pre-amp tubes, is it alright to remove the front of the head, (like beneath the Channel settings), the grid thing?
#8
You can try plugging it into a separate extension cab.

Does your amp look like this basically in the back? It looks like you'd have to slide the chassis out to access the preamp tubes. Not my type of amp

Not sure if taking that front cover will allow you access. I would Google 'Mark V tube change' or something.




maybe someone else will jump in here and help - like I said I have very little experience with these.
#9
Yes very similar to that picture, like the pre-amp tubes are further back and impossible to reach. Do I need to remove the Power tubes first? Unfortunately, I can't get my hands on another cab atm. Thanks for trying to help, greatly appreciate it.
#10
on a few of my different amps throughout time, i have been convinced i have had a microphonic preamp tube, but two out of three times, it was a fatigued cable. the other time, it was a microphonic preamp tube.
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#11
You may have to remove the power tubes to access the preamp tubes but that won't really help because you can't do the test unless the amp is turned on. In other words, you can't tell by looking at the preamp tube. You can probably pull the outer 2 power tubes (and run at half power) so that might give you bit of extra room to get a pencil in there to tap. I really don't recommend that though unless you can get someone else to confirm you damage anything. If it were my amp that is what I would do.

Actually, what I would do is just unscrew the right screws and pull the chassis out of the headshell so I could access all the tubes properly. Unfortunately, both of these things I'm bringing up can be dangerous. Maybe search/ask on the Boogie boards.

This amp should be under warranty no?

Take it to a qualified tech if what I'm saying is a bit much.
#12
Check ALL cables first


If you are at all uncomfortable with removing the chassis, then take it to a tech. And not a "tech" at GC. Small shops are best for that sort of thing.
I highly suggest in your case to take it to a tech.
But...

If you have no issues with removing it, go ahead. BUT BE EXTREMELY CAREFUL. DO NOT TOUCH ANYTHING ON THE TOP SIDE WHERE THE WIRING IS. THE VOLTAGES CAN BE LETHAL.
Then you can set it down on a table (A non metallic table top). You can then easily hook everything up and do the pencil eraser bit.
Another thing you can do at this point...
Get some "DeoxIT" or similar product. Its basically like contact cleaner on steroids.
Unplug everything.
Pull out each tube, one at a time and spray some DeoxIT on the tube pins.
The insert and remove the tube from its socket several times.
Do this for each tube.
DeoxIT evaporates quickly but I usually wait about 15 minutes after doing this before I plug everything back together and test the amp.
This cleaning process can possibly fix the problem.
Its a good idea to do this when putting new tubes in as well.
#13
Check easier things first such as the cables, speakers, pickups & wiring. When those check out, do what 311 and codemonk suggested.
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