Problem with Mark IIB

[James]

Hello,


I've had a Mark IIB for about a year, but recently I noticed that one of the power tube sockets are starting to get real loose..And they might eventually fall out.

I'm a bit worried because the tubes are pretty old, and if I have to replace them, I don't want to make the problem worse or short anything out.

I used to have a Dual caliber DC-3, and I had the exact problem, but it completely died..

Is there a way I can tighten the tube socket or something?

There's one thing I can see, those little things around the outside of the socket are bent out of place, but I'm not sure if they should be tightened.

I'll see if I can get a photo of those little bent things,



Thanks.

 

[BPski]

Yes, it sounds like your tube sockets and tube clamps have loosened up. This is an easy quick fix for a tech. The individual sockets where the pins enter must be "bent" to restore their shape making them tight again. While the tech is there the sockets should be cleaned as well. Lastly the clamps should be also "bent" to restore their shape to grip the tube's base to relieve the stress on the tube socket and keep the tube where it belongs. You can try this yourself just be careful not to bend the sockets too much or they may collapse or bee too tight. Also bevia careful because some of the pins are connected to the power supply (plates and screens) and there may be some residual voltage lingering in the filter caps. Mesa uses resistors to bleed off this voltage but it is always better to be safe.

I hope this helps.

 

[James]

Thanks, I'm taking it to a tech soon.


Also, someone told me that the Mark IIB doesn't have a bias...Is that correct?

 

[BPski]

No bias adjustment on the Mark IIB. Go to Mesa's site and go to the Articles link. There is an article about bias there.

 

[James]

Ok, that's good then!


I'm trying to replace the pre-amp tubes at the moment, it has one of the original 1980's ones! :shock:


It still sounds killer though!


Thanks for your help everyone.

 

[RR]

Thanks, I'm taking it to a tech soon.


Also, someone told me that the Mark IIB doesn't have a bias...Is that correct?

Yes, take it to a tech let him fix it.

Yes, Mark IIB have a fixed bias. You should phone M/B and asked what tubes they recommend on your Mark IIB and they'll respond with STR-415 (I think) of Sylvania Tubes. Get these tubes even if you have to spend a little more.

From a Guitar Player Magazine in roundtable of amp builder which includes Fender, Marshall, Mark Goodman of M/B claims original Mark Series were build around the Sylvania 6L6s and they don't really sound as good with other tubes.

O-kay, I'm just quoting from this magazine so I could be blowing hot air.

I too have a Mark II-B and only have two sets of Sylvania Tubes. ANd this is a 300 Series Colesium amp (six 6L6s of Sylvanias). Only the effect loop was modified (by Mark Benedelli [msp?]).

 

[James]

I can't find ones called STR-415's on the online shop, did you mean the other ones?


I'm a bit concerned about buying Mesa/Boogie tubes, I had bought some before for my Subway Rocket (EL-84's though) , and they lasted for about a week.

That didn't happen with the sovtek tubes I stuck in there after :?

 

[RR]

http://forum.grailtone.com/viewtopic.php?t=1210

You might have to phone MESA directly and mention you have an original Mark Series amp.

 

[James]

Ok then, I'm using the EHX 6L6 tubes at the moment...I'll replace them sometime.


Hmm...If I changed the preamp tubes, I wonder if it would sound better.

It currently has one original 1980's boogie tubes.. (russian?) preamp tube, the rest are unbranded chinese ones I think.

It sounds unbelieveable at the moment, but I wonder if it can sound better?? :?


If I replace them sometime, what should I get?


The amp is in pretty rough condition, so I don't want to screw anything up.

http://www.unofficialmusicsite.com/gearpics/amps/DCP_1031.JPG

http://www.unofficialmusicsite.com/gearpics/amps/DCP_1032.JPG

Oh, and you can see a non-original boogie footswitch on top of the kustom cabinet, what kind of cable are you supposed to use for them? regular guitar cables?

 

[Boogiebabies]

Mesa has the STR-415. $ 85.00 a bottle. Cooler than hell to have the original tubes in there though. Nice high end and a fat bottom. These are probably rated for 10,000 hours. Anyone care to guess?

 

[LHanson]

I can't find ones called STR-415's on the online shop, did you mean the other ones?


I'm a bit concerned about buying Mesa/Boogie tubes, I had bought some before for my Subway Rocket (EL-84's though) , and they lasted for about a week.

That didn't happen with the sovtek tubes I stuck in there after :?

I think Boogie tubes have a 90- day return policy.

 

[Rich M]

Mesa has the STR-415. $ 85.00 a bottle. Cooler than hell to have the original tubes in there though. Nice high end and a fat bottom. These are probably rated for 10,000 hours. Anyone care to guess?

$85 EACH!!!! No wonder they have a fixed bias. Make you a dependent junkie for their overpriced tubes. Take it to a competent tech and have them put an adjustable bias in there, by some quality NOS tubes (at a fair price) and set them up right. I've read Mesa discourse on fixed bias and what I got from it was your either gonna get screwed by the amp tech adjusting your bias or by us screening a bunch of tubes. We think it is much better if you let us screw you. If your neighborhood is crawling with crooked techs, they might be right, but if you have a competent, honest tech, you should be able to get the amp set up for less than $85/tube. Just my opinion.

 

[RussB]

Rich M,

Mesa STR-415's are Sylvania 6L6GC's. KCA has them for $125 a pair...

http://kcanostubes.com/content/esto...L6/7581/5881/KT66/EL37,6L6GC,&catidarray=3,6,

You can pretty darn close with JAN Phillips 7581A's, but they will still run you $100 a pair. I have a quad of these in my MKIII, and am quite happy with them. My MKIII has an adjustable bias setting added to it. The control grid resistors to the outside pair were also swapped out to 82k

$85 is a bit high, but if you MUST have the bottle printed "MESA STR-415", go for it! Mesa also offeres a good warranty on their tubes as well

 

[Rich M]

I'm not gonna tell folks how to spend their money. But for $40 you can get a bias probe and never have to pay a tech for biasing your amp again. Think it is out of whack? Check it. No charge. Mesa (like KCA) bases their price on what they feel the market will bear. I'm fine with that. Spouting BS about bias pots failing and that's why we use fixed resistors takes advantage of folks who don't know much about these things. If they're worried about failures, why don't they use a sealed bournes cermet 20-turn trimmer? If it's good enough for the military, it's good enough for me. It's not like they're amps are cheap. And whats with the plastic pots on the front panel? I just bought a Mark IV with three of them cracked off. THe only good thing was they were cheap to replace (I'll install them myself). But you'd think if they wanted to keep their customers from getting screwed by techs, they'd put some quality there. :twisted: :twisted:

Bottom line, I've been pretty much a marshall guy up til now. I got a used Mark IV cheap and after a fair amount of messing around, I'm able to get some good sounds out of it. If I were to follow Mesa dogma on running this think, it would have me broke in no time. PReselecting tubes is one solution to the biasing problem, but not really an optimal one IMHO.

 

[RussB]

Your loosing me Rich...I don't quite get what all the ranting is about!

Broken pots on a (cheap!) used amp? That sounds to me like abuse, not a manufacturing issue. All amps break when they're beat on...the more knobs and gadgets, the more there is to go wrong!

Non-adjustable fixed bias...love it or hate it, that's MESA. All the tube retailers can sell you tubes that operate in the "Mesa" spec's without a problem or extra costs. Not really a big deal. IMHO.

On thing about the whole bias issue is the "Simul-Class" factor. It's tough to CONSISTENTLY adjust the bias on dis-similar tubes...like I said, I have added a bias pot to my MKIII, but I must also swap out resistors with each tube swap, or add yet another bias pot or two, all of which become interactive! Add to that variable power selection (class A, triode, pentode, tweed) It gets very complicated, very fast.

 

[Rich M]

Am I ranting? :?

Pots are broken clearly due to abuse. However, you spend $2K on an amp (I didn't) you'd expect high quality components, not pots with plastic shafts that break fairly easily. There is a well known issue with Mesa amps failing for a variety of reasons(see other thread). I like the amp and Mesa in general, but they're not listening to their customers.

Back to bias. Agreed that with all the stuff in a mesa power amp, you don't want to try and balance tubes, but you can match them and use an adjustable bias to bias them correctly. Relying on dealers that will match to MESA's bias voltage (after doing a sufficient burnin to avoid drift) precludes a number of sources for NOS stuff (including shameful roadside pickups). Not your bag? Fine pay $85/tube. It is interesting though that your amp has an adjustable bias

Again, we can argue all day about this,and I really don't want to. Mesa approach is a simple one for folks who don't know or care about how amps work. It's akin to apple computers. "Easy to use" is what I hear about these new fangled contraptions. As long as you get your hardware from the apple dealer, get it serviced at the apple service center. Don't get me wrong, they have their place, just not on my desktop.

Really the thing that I object to is them selling it to the public as a reliability issue, which you'd have to agree is BS. If not, you better get that flaky pot out of your amp.

Anyway, maybe I am ranting...a little bit

 

[James]

Those old tubes are expensive...any new ones that are good?

Maybe some JJ's or something.

I'm in no rush to get some new tubes, but I can't tell how long these EHX ones are going to last. (the previous owner put them in)

I'm defenetly going to replace these preamp tubes, they're pretty old apparently.

The amp sounds a bit weaker for some reason, it's just as loud, but it's starting to sound weak and fuzzier. (It's hard to notice, but still....)

The mid's have dropped a fair amount, the low end is all muddy, and there's too much high end. :?

I haven't changed anything at all with it, same speakers, same settings.

I'm not worried about it, just as long as that means there's no big problem.

I *think* it could be the different type of pickup on my new guitar, but I didn't think this amp was really 'picky' with guitars.

I'm starting to dislike the sound of these celestions in the cabinet though.

 

[James]

OK, the Mark IIB is at the amp tech right now, getting the sockets tightened and cleaned...As well as a complete check-up...The tubes I've chosen are four chinese 12AX7A's and two...Well, I haven't called up Mesa/Boogie yet, I'm broke :evil:


I believe this amp is COMPLETELY original, should I get any caps replaced?

I really can't tell if there's any problem with it, it's nice and quiet...Though it's been sounding a bit weak, which is why I brought it in. The old preamp tube is on it's last legs probably.


Here's a picture of its guts: