Mesa Boogie Studio .22+ (older model) regarding A/B switch

JayP

Member
Messages
8
On the back panel just under the power cable is a rocker switch(seen pictures with toggle switches) I just bought this amp from a pawnshop on ebay. When I powered it up it sounded great, punched the channel switching footswitch and no problem, worked fine. I was under the impression the toggle switch was just a manual switch for the lead to clean but not here. This rocker switch is in the "B" position and when switched it totally loses power. When I contacted the seller, he also thought the switch was just a manual lead/clean switch and didn't bother with it since it had a foot switch. Does anyone know anything about this function, I've looked everywhere and nothing is explained about this switch, I'd appreciate if anybody knows, and yes I'm gonna buy new matching tubes next.
 

Jeff Gehring

Gold Supporting Member
Messages
7,671
If the switch you are talking about is located below the fuse post on the back, and has the word "ground" above it, it is a switch that connects one lead of a cap to either the AC hot, AC neutral, or neither. The other lead of that cap connects to the chassis.

If throwing that switch affects anything about the amp, stop. Unplug the amp. You have a problem that needs to be dealt with BEFORE you play the amp any further.
 

JayP

Member
Messages
8
Thanks Jeff, I just knew there had to be more than a dead switch, plus I can tell the chassis was removed at one time because you can feel a burr on the screw heads. I guess it all depends on what kind of money I have to spend on it to determine if I'm gonna send it back. I have a Mesa DC 3 also I need to have looked at too. probably sell that one.
 

JayP

Member
Messages
8
Thanks Patrick but I couldn't make heads or tails of a schematic and I've read the manual a couple of times & it don't say anything about that switch. I read somewhere that one of the models had a switch that allows the amp to use a built in EQ but I think it was a new unit, I'm just taking it to my friends shop they have one of the better techs in Houston. At this point I'm more worried of how much this is gonna cost me, I have another Mesa I wanted to re-tube, kinda ticks me off.
 

Blue Marvel

Member
Messages
1,159
As mentioned this is a ground switch. Some older amps had this option, it came from Fender designs IIRC. The best thing to do is disconnect it to where the amp has a solid ground all the time. Make the ground wire go straight to the chassis, disconnect the switch, and remove the cap. The cap that is wired to the switch is sometimes referred to as the the death cap for the reason you could get killed if the circumstances are right and the cap is switched on.

This is a simple fix.

BTW these are great amps I have one.
Congrats!

Mine has the lead drive mod, the C12 cap clipped on the lead channel, and a WGS G12C/S installed in it. I love this amp!
 

JayP

Member
Messages
8
Thanks Blue, I hope that's the problem, will the ground switch work or does it need to be wired like it came originally? I kinda hate not being able to switch it, you know how some stages can be some time. What's these mod's? Is it worth the effort? Another question I've read something about EL34's and EL84's can it use either? It has EL34 now
 

Blue Marvel

Member
Messages
1,159
The mods in my ooinion are must have for the 22+ Mine has the lead drive mod which gives you a preamp gain control over the lead channel. It also has capacitor C12 clipped which removes that insane amount of midrange boost on the lead channel. With those two mods for me it makes the kead channel useable and really good sounding.

Mesa will perform the lead drive mod for like $130.00 bucks including shipping. They will not mod the EQ of the lead channel though its just a simple cut one leg if that caoacitor or remove it all together. Some put a switch in to bring it in and out if the circuit. I cant stand the mid heavey cap so I removed mine.

I also got my 22+ recoverd by Mojotone in a custom color with new grillcloth. It looks awesome.

And last but not least I replaved the 30uf filter caos with 47uf Nichion caps. It made a slight difference in the amos bottom end.

And I installed a WGS G12C/S speaker in it. The darn thing sounds like a dream now.
 

JayP

Member
Messages
8
I'd like to have mine recovered, saw the cane grill cloth on eBay that was cheap. Planned on a Celestion I have one in a Mesa DC 3, freakin loud. Thanks guys sounds like some good stuff for me to try, see ya soon!
 

JayP

Member
Messages
8
Hey Blue Marvel, sorry I've been away for awhile, been in Phoenix visiting my older brother, he has cancer and not doing well at all. I'll be going back sometime in February. That's some good stuff to know, thanks for sharing. If Mesa will do that mod for $130 that sounds pretty good to me, I'll get in contact with 'em and see what I can't get worked out. I quite sure I'll have to replace the tubes, probably buy 'em somewhere besides Mesa, I see them on ebay all the time for under $100.
Do ya remember about what you paid for a recover, think I'll look into that and a cane grill. Thanks again!
 

Blue Marvel

Member
Messages
1,159
Hi Jay,

Yes Mesa charged me $130.00 for the mod including shipping the chassis back to me, I had to pay for the shipping to them also. I think Mojo charged somewhere around $200.00 or so for the recover IIRC, they did a great job!
 
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Blue Marvel

Member
Messages
1,159
Oddly enough I must say for years I overlooked these amps but it has become my good friend, my trusty companion. The tone of the the thing is out of this world, its amazing there isn't a cult following on these. And the real secret is how light it is.
 




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