Please Help Me Troubleshoot a Mark IV Problem

[ronmail65]

I just got a used Mk IV head, made in the 1990s.

Great tone, but there is a low crackle after a chord fades. Additionally, the decay of a chord has a fizzle quality, kind of a crumbly sound -- not a smooth even decay. The higher the gain settings, the more pronounced this is. I get the same issue in all channels. It guess it just sounds weak. It has 2 6L6s in the middle and EL34s on the ends. This is how it sounds in Simulclass. The amp is otherwise clean and has no apparent issues.

Based on my previous experience with one of these amps, it sounds like it needs new tubes. What do you think?!??

Follow up question... if you also think it needs new tubes, what do you recommend? I want a sound that is good for hard rock - vintage and modern gain tones. I don't have much use for shimmering cleans.

- Thanks

 

[LithiumZero]

I've owned 3 boogies and have noticed this about each of them even after complete retubes. The decay is not smooth. It really has never been a problem on stage or in the studio but it's definitely there. Anyone else have any ideas?

 

[MrMarkIII]

Sounds to me like a voice coil about ready to give up the ghost (furry sound as the note dies away). Have you tried another speaker?

 

[ronmail65]

Thanks for the reply, but this is definitely noticeable. Almost like playing through a cheap little speaker that has a tear in it.

 

[ronmail65]

The problems I described occurred while testing the amp in Tweed power. On Full power, the amp just emits an endless screech. If I turn the volumes all the way down, the screech just keeps coming.

When I switch back to Tweed power, now I get the screech there too. Sometimes I can play a few notes before it starts. When the screech starts, the amp doesn't take any sound from the guitar nor is it modified by any changes in the knobs -- the only way to stop it is to turn the amp completely off. It's as if the amp is picking up an entirely different signal.

Help!??!? It's unplayable.

 

[ronmail65]

The problems I described occurred while testing the amp in Tweed power. On Full power, the amp just emits an endless screech. If I turn the volumes all the way down, the screech just keeps coming.

When I switch back to Tweed power, now I get the screech there too. Sometimes I can play a few notes before it starts. When the screech starts, the amp doesn't take any sound from the guitar nor is it modified by any changes in the knobs -- the only way to stop it is to turn the amp completely off. It's as if the amp is picking up an entirely different signal.

Help!??!? It's unplayable.

 

[Buddy]

Find a friendly TECH style person .
Many of us find them Useful in situations ...just like these ...

 

[darknewmark]

the mesa boogie website has an article on how to diagnose tube problems and in some instances to solve them rather easily. If the problem occurs on all channels and is tube related it will likely be the driver tube (the one with the cover on it) or it is one or more of your power tubes. Tapping the tubes in question with a chopstick with the amp on to check for changes in the "screech" might help to diagnose which tubes might be causing the problem. I hope this helps and I could right pages about the subject but I believe this may prove a viable shortcut in conjunction with the mesa web site if my advice doesn't solve the problem. Take into account that a set of tubes is usually cheaper than a tech for any task and may resolve the issue.

 

[LEVEL4]

I'm certainly no amp expert, but I recently bought a used DC-3 and started playing around with switching around my TungSol preamp tubes into other sockets (with some unexpectedly good results). After one tube switch, I got crackles and volume variances. Upon further investigation, I noticed that I hadn't completely seated one of the preamp tubes all the way in its socket. Have you tried simply re-seating each tube?

 

[phyrexia]

So does the amp make this noise when nothing is plugged into the input? If you turn all the preamp knobs to zero does it make this noise?

oscillation = bad cap sometimes

 

[guitardude05]

i was just about to post something related to this. the decay on mine makes the crackling noise that you described. i hate it. sounds like a blown speaker at some times, but i know its not because ive replaced the speaker about 6 months ago.

if that part of the sound was gone, i would love the amp. i found that putting the 240 and 2200 eq sliders way down helps get rid of this sound, but is still a little bit there.

 

[bryan_kilco]

I have noticed a slight sound with the decay in my MKIV as well.

I thought it was my gate pedal at first, but its not. It almost sounds like a slight tiny bit of reverb ...but...not quite. Isnt too noticeable unless you are at high volumes and do a quick chug and stop.

 

[ANIMATED SUSPENSION]

The 'fizzy' decay thing, is not unusual it happened with my Marshalls. It should only occur however, at low volume with high gain settings. Once you let the power amp contribute more it disappears. If it doesn't then there is a problem with it !

 

[Restless Rocks]

Suspect would be dirty pots, (rotate all the controls rapidly back and forth then reset). The screetching sound is most likely a microphonic preamp tube. Does this occurs when you have the reverb on? (could be a bad pan or cable to reverb pan). There are certain types of Russian made tubes that simply don't work well in Tweed mode due to the lower voltages. And then there are coupling caps and cold solder joints which are really sometimes difficult to isolate. And among other possibilities are failing LDR's and oxidized relays. I've also had power tubes make this kind of rumbling decay after they've been beat to death in transport. (The innards simply get loose) New tubes for sure and check that the sockets are tight. The power tube sockets often get wrangled out and need the contacts tighted.

 

[ronmail65]

PROBLEM IDENTIFIED AND SOLVED -- BAD POWER TUBES.

Yes, the tubes were very old. In fact, discontinued by Mesa over 4 years ago. "Very old" and "Very worn" were the words of the technician.

Of course the butthead who sold me the amp swears it was "perfect" when he sold it and that something happened in shipping.... like maybe the amp got put into a time machine and was aged and extra 7 or 8 years... or someone opened the box and played the amp at full volume for about 100 hours then packed it up and delivered it to me.

As "proof" he also sent me some audio of the amp before he sold it. Apparently, to him, a "perfect" amp sounds a lot like putting dog crap in your ears.

 

[trem]

When buying used amps, it's a good practice to ALWAYS assume that the tubes are shot and hence need replacing.