Mark IV Volume & tone fluctuation problem.

[Mesa-arty]

Hi all,

Ive had my mark Iv amp (1x12 combo version) for about a year now it was made in 2001, all the power tubes in the amp are brand new and the preamp tubes are about 6 months old. Ive been having a problem with my amp's volume and tone, while playing with my band or practicing i notice the Volume will get higher and the tone will get muddier and not as good then it will eventually get back to normal. ive tried different cables even a different guitar. and it still does it. It also seems to happen at completely random times so i cant get the amp to mimick this infront of an amp tech cuz it happens totally randomly. I could play for hours and i wouldnt here anything wrong and sometimes i can hear it as soon as i turn the amp on. Ive tried to lightly tap on the tubes to see if that changes the sound and the tubes seem fine. (Regular unmistakable orange glow). I opened my amp's chasis and i cleaned the inside with electrical duster cleaner, i cleaned the tube pots really well in and out. It had alot of dust and even hair in it, after i put it all back together i played my amp for about 4 days without noticing any kind of fluctation at all, i was happy to think i fixed the problem and then all of a sudden today it started doing it again!!!!

This is very frustrating, my amp sounds awesome but when this random fluctuation occurs it sounds horrible!!! PLZ PLZ PLZ anybody that knows how i can fix it or knows any other troubleshooting tips for me any advice would be greatfull! Thnx for reading

 

[ryjan]

Did this happen before you replaced the power tubes also. There's an old mechanic's saying, "new doesn't always mean good, just clean"

 

[Mesa-arty]

Thanks for your reply. Yes this happened before the new power tubes were bought... the reason i bought new power tubes was because of this problem. I thought the power tubes were wearing out even thou my old set of tubes were only 6 months old. Still looking for any helpful replies would be much appreciated.

 

[ryjan]

Do you use a good power conditioner? Before I got mine I thought my amp had problems because of all the little pops and crackles. Turns out it was just the wife and kids running around and flipping light switches and running the dish washer etc.

 

[Mesa-arty]

Well ive noticed some pops and crackles here and there also thats just interference for example my keyboard LED light makes my amp whistle when the guitar is near it.... i've used my amp at home and at my rehersal warehouse it does the exact same thing at both places. When i opened my amp i didnt notice any bad solders or anything, does anyone think this may be a preamp tube problem or still my powertubes?? ive already been through 2 sets of power tubes because i thought the tube was the problem in the first place... and also could this be a bias problem even thou the mark iv is a self baising amp. Whats really frustrating is that i cant replicate the problem im having infront of an amp tech so i cant even explain to them whats happening. It happens at completley random times. The amp sounds great and then all of a sudden a dramatic volume increase with muddy tone and after a bit the volume will swell dramatically and then eventually return to normal. I also see that a few ppl have had this happen on the forums here and i wasnt able to find any solutions yet. Any more usefull advice would be apreciated.

 

[Tuna141]

My first guess would be a bad tube. I'd try swapping out your preamp tubes one at a time to see if the problem goes away.

To check the power tubes, you can also run in Class A which will only use the outermost pair of tubes. If the problem goes away, you can assume that there is a problem with one of the inner set of tubes.

Good luck.

 

[swbo101]

I never use the reverb in my Mark IV A that high. Usually no higher than 3 or 4, I really don't like the sound of it. However, I would check the V4 pre-amp tube (12AT7). You might be getting a hum from that tube. Is it old? If not that just maybe the way it sounds cranked high up, I know many don't like the reverb in this amp.

 

[Mesa-arty]

Guys i found out that when i sort of tap on the Equalizers on the front of the Mark iv it changes... i can make the fluctuation come and go. Do you think the EQ is the problem causing the fluctation?? Has this ever happened to anyone else?? Plz let me know if anybody can help.

 

[SonicProvocateur]

I opened my amp's chasis and i cleaned the inside with electrical duster cleaner, i cleaned the tube pots really well in and out. It had alot of dust and even hair in it, after i put it all back together i played my amp for about 4 days without noticing any kind of fluctation at all, i was happy to think i fixed the problem and then all of a sudden today it started doing it again!!!!

Yeah, no amp should have hair in it, especially a Mesa. That's why they come with dust covers. Sounds like the previous owner might have owned animals and didn't take good care of his amp. Sounds like more cleaning might be needed. Ask Monsta-Tone how it would be best to clean it out for hair.

If the GEQ itself is the cause it might be a short or something. If the amp is being microphonic it could also be preamp tubes or a dirty jack. I'd still shoot him a PM or call him.

 

[Mesa-arty]

Ok i already cleaned all of the dust out. i just want to know if this could be because of the EQ on the front and if i can fix this or if this is a bigger problem. I will give Monta Tone a PM thnx for ur advice bud.