3 problems with my mark IV

[pie4peace]

Hey all,

I got 2 problems with my mark IV:

On clean and rhythm 2, when I put pretty much bass on it, I get a weird humm and crunch (not good crunch) when I play my low strings. Is this a problem of the speaker or the amp (mark IV combo). I get it in both Class A and Simul Class...

Then on my lead channel I get a weird humm when I dont play, like my amp is about to explode, a very bass crunched noise.. I think it has something to do with the guitar input in the amp, because the sound changes if I move a bit with my cable. Could the input also be the reason for my first problem?

When I put my guitar volume on 0, and my amp master volume on about 2.5, and I pull the Pull bright from my lead drive, I sometimes get a high feedback sound, a really high note... When I pull it back in it gets less....

Anyone knows the reasons for these probs and how to fix them/how much it costs to fix them? I put in new tubes about 6 months ago...

Grtz

 

[primal]

Sounds to me like you should take it to a tech since you have already replaced the tubes, but I will let you in on my experience with a similar prolem

I had a weird humming problem with mine as well. Heard it on all channels, but more prevelent on lead, "I think" due to the natural compression of distortion.

I had read that imbalanced power tubes were the most common cause of hum, especially hum that swells over time.

It only happened in simulclass, not class A.

HOWEVER, I swapped my inner and outer power tubes (I was using all 6L6), and it started happening in both Class A and Simulclass. Replaced power tubes, she is as quit as could be.

The other stuff with the low strings an high bass, no idea.

 

[stephen sawall]

Did you try a different cord ?

Did you try changing the tubes ?

Did you go thru the recommended stuff in the manual ?

http://www.mesaboogie.com/manuals/Mark%204.pdf

 

[pie4peace]

Cords don't change anything, the power tubes are new and the manual isn't of any help... I'll just take it to a tech soon...

 

[angelo]

Cords don't change anything, the power tubes are new and the manual isn't of any help... I'll just take it to a tech soon...

If you want to --- you may look into the preamp tubes to problem shoot that way first.

First - Did this problem happen SINCE you put in the new power tubes or was it there before too?

The manual talks about the reverb tube. Do you have the reverb on? Does it happen with the reverb off?

The v1 preamp tube may also be an issue since it seems to happen in all gain modes.

Personally, I'd rule out the preamp tubes before going to a tech... for any amp.

 

[Platypus]

Definitely rule out tubes before going to a tech... even new tubes can be bad.

 

[stephen sawall]

Definitely rule out tubes before going to a tech... even new tubes can be bad.

+1 .... new does not mean good. Most of the problems are from preamp tubes. The only way to test them is use a tube that works fine in a other amp and change out one at a time.

This may not be the problem. But why pay someone else to find out ?

 

[pie4peace]

If you want to --- you may look into the preamp tubes to problem shoot that way first.

First - Did this problem happen SINCE you put in the new power tubes or was it there before too?

The manual talks about the reverb tube. Do you have the reverb on? Does it happen with the reverb off?

The v1 preamp tube may also be an issue since it seems to happen in all gain modes.

Personally, I'd rule out the preamp tubes before going to a tech... for any amp.

Sorry I forgot, but yes, the problem isn't new indeed, but it dissappeared for a while when I put in new tubes...
The thing with high bass = noise is new though... the super noise with overdrive I had before.
I'm thinking it might be the tubes indeed, but the problem is it only accurs when I'm playing for like 1 hour. When I put it on standby and off for a while it's gone, but comes back faster than before.

The thing with high bass isn't occuring on low volume levels, but it comes on higher volumes.

My amp is now at the band's repetition room, so I can't check it just yet. I still have 1 reserve pre-amp tube and my old powertubes, so I can swap them 1 by 1 to see which one fails. It'll take some time though cuz I have to play for like 1 hour to get this. With my old tubes the problem occured faster, like after 10 min of playing, medium volume. I'll check it as soon as my amp is home again and then I'll post what I discovered.

Thanks for the help everyone, if anyone knows what the problem is with the bass-noise, please post what you know, a friend of mine mentioned it could be the speaker or speaker cable, since the higher stringers work perfectly fine, could that be true? With silent recording to a PA panel -> monitor I don't have the problem, but I only played that way for 20 minutes, low volume. But even if i got the problems fixed, I'm going to a tech with good knowledge about old amps (mine is a early mark 4, 80's, and I don't know much about inside of amps myself) and he has some nice NOS stuff, cuz my mark IV has to be ready before august for some gigs! And I don't want any noise on a gig

 

[stephen sawall]

If the problem takes a hour it sounds like you well be taking this to a tech to me.

 

[mrd]

If the amp is that old, it probably deserves to go to a tech for a standard check-up anyway, to make sure the caps and everything are in good working order. It sounds like your amp is +20 years old, so everything in there is likely just plain old worn out. I've never owned an amp for +20 years, so I don't know first hand, but I've heard that replacing faulty caps can be a night/day difference in tone, akin to replacing power tubes that are shot to ****.

I'll second the suggestions about checking the pre-amp tubes, though. If you look in the MKIV manual, there should be a diagram about what each position does in terms of tone. The cleanest/best sounding (maybe even lowest gain, if you like that sound, like an ECC81 or ECC82, rather than an ECC83) pre-amp tube should be in V1 slot, because it's in effect in all channels, and any deficiencies that show up in here in V1 will be magnified possibly many, many (like in the high-gain lead channel) times over before the signal is sent through the power-amp.

Just out of curiosity, how high are you running your bass knob?

 

[pie4peace]

Just out of curiosity, how high are you running your bass knob?

about 6-7 on clean and boosted up and extra boost with GQ..
on lead it's 3-4

amp is still not back at home had 3 repetitions with band last week...

 

[mrd]

That's pretty **** bassy man... do you guys not have a bass player in your band? Even without the GEQ, 6-7 on the bass knob on the clean channel is some very significant bass. I usually run mine at about 4-5 with no GEQ. It might be that you've just wrecked your speakers? Have you had a close look at them?

 

[pie4peace]

That's pretty **** bassy man... do you guys not have a bass player in your band? Even without the GEQ, 6-7 on the bass knob on the clean channel is some very significant bass. I usually run mine at about 4-5 with no GEQ. It might be that you've just wrecked your speakers? Have you had a close look at them?

We have a part time bass player, he usually plays rhtyhm guitar. On the non-solo songs he takes the bass mostly. I checked the speaker quickly once but I was just checking for scratches (I dón't know the word in english) on it, or other errors, but found none. How can you see you wrecked your speaker? I have ordered an orange 4x12 cab and if i don't have the problem with that one I guess it'll be the speaker, no? I'll be able to play the cab monday, when I have the bass problem I'll quickly change to the cab and see if I still have it. I'll post again then

 

[pie4peace]

Euhm I just read that the V4 must be a 12AT7 tube, is that right? Because I think I didn't notice that when I was searching about new tubes, so that could be the reason.

Could a 12ax7 in the V4 slot cause humm and weird noises on lead channel? The first thing I'll do when we play with the band again is turn the reverb of when I'm having the problem!

 

[stephen sawall]

Some of the early IV have a (AT) in them at the phase inverter position. I have one and have run a (AX) with no problems with mine.


..... I think this is true. I am doing this from memory.