Mark IIB 'problems'...what would help?

[Luckyman]

Hello there! Nice to find a forum dedicated to the real thing I'm a Mesa fan from Finland and am seeking for a advice from you gurus.

I've owned Mark IIb Combo with EVM-12L for about 15 years now, and I haven't gigged with it that much, and have had long periods that I haven't used it that much. Anyway, now I'm back in the home studio/band scenes again and have dived deeper into the soundscapes of my trusty Mesa. I know that it can deliver, but the more I play it now, I think there's something wrong with it..

It seems that I cannot get the cleans as they used to be. The sound is somewhat muddy and distorted even in when the Vol. 1 is set to around 3-4 or so (using my Fender Tele). Overall the amp sounds boxy, there is no warmth in the sound. Then there are some really harsh trebly sounds from the E & B strings that also peak even when presence is set below 5 and treble below 6. Bass sounds are boxy, and then is some weird 'clang' sound when I hit the bottom E in my guitars.

Also, it really seems that the longer the amp is on (hours) the sound becomes more harsh and the sounds run out of power and responsiveness.

When I tested the sounds I used my Fender Standard Tele, and didn't use even the EQ.

Some years ago I got some NOS Philips tubes, but the pre-amp tubes must be pretty old...maybe original.

What could be the problem with the amp? I'm seriously thinking about completely re-tubing the amp and seeing if that helps. Can't do no harm, can it What brands and mail-order dealers would you guys suggest for tubes? JJ's?

Other option could be that the speaker would need to be re-coned (?) The speaker is the same that came in the combo, but I'm not sure that around here anyone could re-cone it. Should I maybe buy another speaker instead?

I would appreciate it very much if anyone has any clue about what could be wrong with my amp. In the end, I would only need to use the clean channel, since I get my overdrives/distortions from my effect pedals. Need I say that the overdrive channel in my Mesa was always pretty bad...very out of focus, muddy, and not dense at all.

 

[jvk]

Sounds like you need new tubes, how the volume changes with time is a dead giveaway, so I'm betting on that from what you say. As the faulty tubes heat up over a period of time while you play, they behave differently.

For preamp tubes, I use Tung Sols and a balanced JAN-Phillips 12ax7 for the V5 phase inverter position. As for power tubes JJ is fine, I prefer winged "C" SED 6L6. As your amp is probably fixed bias and was intended to be used with Mesa tubes, I'd go with JJ who can match tubes to your amp so that it can operate with the correct bias.

Sorry if this all sounds a little too much, welcome to the world of tube shopping and biasing To keep it simple you can just buy something like Tung Sol 12ax7 tubes (the preamp doesn't need biasing) and use Mesa power tubes which are average in sound quality, ok in construction quality/longevity but they will drop right in without the need for biasing.

For reviews of different tubes and their tonal characteristics search on this forum, or let google be your saviour.

 

[Eddy Scheepers]

There we go again.... You're not the only one. Have a look here:
http://forum.grailtone.com/viewtopic.php?t=20999

I ordered new capacitors and I'll let you know if it helped me.

Eddy Scheepers
Belgium

 

[Luckyman]

Thanks Eddy (and the other guys for the tube info) advices!! I'm very grateful. I think my problem really sounds like a capacitor prob, since my amp has surely been sitting without use for long periods of time... years, at some point.

If you Eddy could let me know about your experiences with the new capacitors, that would be of great help. I would also need to find out from somewhere exactly what capacitor does my amp use so I could look for them. Do you have any pointers.

Also, I took a look at the Eurotubes site, its really informative, and it looks great. Unfortunately the only Mesa model that's lacking from their 'Full Retube Sets' list is Mark II So I think I'm gonna give them a call and ask what they'd suggest for my amp. Lord knows its time to change the tubes, even if my amp's main problems are not related to tubes.

By the way, since I bought my amp used, it didn't come with manual at the time. Does any of you know if one exists somewhere? The only one I found is this:

http://www.mesaboogie.com/manuals/Mark%20IIb.pdf

..and that doesn't seem like very extensive

There we go again.... You're not the only one. Have a look here:
http://forum.grailtone.com/viewtopic.php?t=20999

I ordered new capacitors and I'll let you know if it helped me.

Eddy Scheepers
Belgium

 

[jvk]

Oh and did I mention it could be caps too?

 

[carlosasi]

You may not have to change out the Pre amp tubes. I just refurbished a Mark IIA and had the caps and power tubes re-done, but the pre amp tubes are the originals from when the amp was made and they sound great, the cute little dears.

 

[Eddy Scheepers]

Here's your schematic.
http://www.tubefreak.com/mesa.htm#mark2

I ordered these electrolytic capacitors for my MK IIc+

30UF-500VDC (4)
220UF-300VDC (2)

from: http://www.watfordvalves.com/products.asp?id=3&man=73

According to my schematics, there appear to be more, I'll have to find out. I won't start the installation before I have all relevant parts. If anyone can help, don't hesitate.

Eddy

 

[Buddy]

While you're in cap swap mode you might want to change the bias supply caps also ....

 

[Eddy Scheepers]

Thanks, Buddy. Which ones are the bias supply caps?

The two 50Uf-75V ?

I had already marked these, but not yet ordered.

Eddy

 

[Eddy Scheepers]

Thanks, Buddy. Which ones are the bias supply caps?

The two 50Uf-75V ?

I had already marked these, but not yet ordered.

Eddy

 

[Buddy]

Thats what the schem. say's , but I have no personal experience with the mark II's . I do recall however that in a previous post someone mentioned using higher voltage rated caps there .
Anyone ?

 

[Buddy]

I use a jumper with a resistor soldered inline . + side of the cap(s) to chassis .
You can do it without a resistor , but you get sparky sparks !
Unplug said amp FIRST . Keep one hand away from the amp chassis whilst doing either . 8)

 

[Boogiebabies]

Thats what the schem. say's , but I have no personal experience with the mark II's . I do recall however that in a previous post someone mentioned using higher voltage rated caps there .
Anyone ?

Nichicon 47UF/100V axial.

 

[STUART]

Eddy here's a good source for parts if you looking for caps etc
:wink:

http://uk.farnell.com/jsp/search/browse.jsp;jsessionid=JSTYXP5IFLJNDQFIAEWZKBQ?N=500004+1000224+104093+130075&Ntk=gensearch_001&Ntt=47uf+100v&Ntx=&_requestid=199902

 

[Restless Rocks]

+1 on checking the Caps. One other thing to consider since the amp has been stored for very long periods is that your control pots and jacks could most likely need a good cleaning. Oxidized pots can cause all the symptoms you've mentioned here. Especially the FX loop jacks. Craig's Deoxite is a favorite of many here or any good brand of electronic control cleaner/lubricate. Don't forget about the Presence control on back. Tubes can be stored indefinately without any "aging". Those older tubes may be better quality than some of the new stuff available now.

 

[Eddy Scheepers]

Thanks to all who replied. I ordered two 50UF/100V bias supply caps too.

Eddy

 

[jvk]

+1 on Deoxyit. Wicked stuff. Place a cloth under/around the pots to prevent the stuff getting onto the chassis and circuit boards.

 

[Boogiebabies]

+1 on Deoxyit. Wicked stuff. Place a cloth under/around the pots to prevent the stuff getting onto the chassis and circuit boards.

It loves to seep out of the switches on the pull pots. Amen to the cloth.

 

[Luckyman]

I ordered new capacitors and I'll let you know if it helped me.

Eddy, have you received these yet? Can you tell any improvement in the way that the amp sounds/works?

 

[Eddy Scheepers]

Hello,

After replacing the old (24 years) electrolytic capacitors (4 X 30uf/500V, 2 X 220uf/300V) there was not a noticeable change in sound, but the problem with the loss of quality after several hours of playing was solved. That was a major improvement. There are two other capacitors that I might replace (see second photo in front 2 X 47uf/ 63V), but the negative bias supply voltage is OK (-48V) , so I'll see.. I also changed the first 12AX7 (12AX7A-C by TubeAmpDoctor) and 2 power amp tubes (Matched set of 6L6-GC , by TAD). Again the sound improvement was - to my ears at least - not noticeable. And finally I changed the Celestion 12-65 by an EVM-12L. The amp is in good working order now, the first minutes AND after several hours of playing too.
Have a look at the photos. The large black parts are the replaced caps.
Thanks to all who contributed to this thread.
If anyone has more advice on this matter, please don't hesitate to contact me.

http://users.skynet.be/fa000612/BackUp/cap1.jpg/
http://users.skynet.be/fa000612/BackUp/cap2.jpg/

Regards

Eddy Scheepers