Blue Angel, possible Mojo Module rebuild....

[ICR]

I fix and build amps, and hang out mostly at the amp garage. Yesterday one of my Mesa Rectifier amps stopped working.

It was my Blue Angel that I have had since 1996. Here is a clip of it in action (no distortion pedal) : http://soundclick.com/share?songid=6167091

Anyway, I have yet to get it on to my bench, but I wanted to get any info I could on the Mojo Module (thats how I found this forum).

I got the Mojo Module schematic off the Maverick (I also have a Maverick to look at, to get the transistor values).

I'm going to open it up tonight and see what is wrong. Output section is fine, and effects return is OK. Tubes OK . Seems to point to the Mojo Module, but, I'll see, and post what I find.

If it comes to re-doing the Mojo Module, I'll post as I go, in case anyone is interested in that thing.

If anyone has the transistor values, or anything else to share, please chime in.

 

[ICR]

Here it is ready for surgery...

 

[Aart]

boogiebabies knows his stuff about it. He has one (or a pic) without the gunk over it, so you'll be able to see the correct values.

He should be able to help you, maybe send him a message about it if he doesn't find this topic.

 

[ICR]

boogiebabies knows his stuff about it. He has one (or a pic) without the gunk over it, so you'll be able to see the correct values.

He should be able to help you, maybe send him a message about it if he doesn't find this topic.

Ok, I found this picture, but it looks like my amp is going to be OK after all.

http://img.villagephotos.com/p/2005-2/951008/ba002.jpg

 

[ICR]

Boy to I feel like an idiot. As I had the amp upside down to take the chassis screws out I saw an empty tube socket. Looks like I had "borrowed" one of the tubes a few months ago and never put a new one back.

Since I had all the chassis bolts out already, I went ahead and took the chassis out to check it out and to take some pictures that I will post.

The Mojo Module looks bigger than what I would expect to contain those few components seen on the Maverick schematic (16 or so). With a dental mirror, I counted 85 terminations under the PC board! The components on top were embedded in rock solid black epoxy. Not silicone, like Dumble used.

That previously posted picture of a non-gooped Blue Angel has about 36 components.

Well, this would have been an interesting thread, but at least I get a few months of my life back

 

[JimAnsell]

boogiebabies knows his stuff about it. He has one (or a pic) without the gunk over it, so you'll be able to see the correct values.

He should be able to help you, maybe send him a message about it if he doesn't find this topic.

Ok, I found this picture, but it looks like my amp is going to be OK after all.

http://img.villagephotos.com/p/2005-2/951008/ba002.jpg

thats my pic, and my old blue angel after i got it back from boogie.
they replaced the whole circuit board.

 

[ICR]

thats my pic, and my old blue angel after i got it back from boogie.
they replaced the whole circuit board.

Thanks for posting it. Can you tell me why you sent it in to them (what was the amp doing) or is there a thread on it somewhere?

 

[ICR]

It was dark up there checking the tubes, so I missed the empty socket. Of course, I saw it when I tipped the amp over to undo the chassis screws.

 

[ICR]

I went ahead and took the chassis out just to check everything. I have had this amp since 1996 and it has been trouble free.

 

[ICR]

Here is the underside of the chassis, with a close-up of the Mojo Module.

 

[ICR]

Here is another close-up of the main (only) board.

 

[ICR]

Serial number on this amp is in the 500s.

 

[boogietone]

Uummmm...what's a Mojo Module and what does it do exactly? Is it an aftermarket mod or a mod offered by Boogie?
Thanks!

 

[cgil]

Greetings and Happy Holidays to all. And, thanks for posting that pic of the actual "mojo" circuit! It's certainly interesting to finally see, cuz the pin pattern underneath had me fooled for a long time into thinking it was full of opamps! It's somewhat of a relief that it's really not.

Still, my Blue Angel's long been dead; but I won't be sending it to Mesa for repair because I've become somewhat of an amp mod junky in the process of preparing myself for it's grand P-to-P rebuild operation. And no, I won't be using the mojo module when I rebuild, or mosfets, or clipping diodes, or anything else of that sort.

The iron and the basic power amp design will stay, of course, with a few minor tweaks such as separate cathode resistors and caps just to eliminate the need to be stuck buying matched pairs of tubes. If possible, I hope to incorporate some full/half/quarter power switches (a mod from EL34world & 18watt.com) on the cathode bypass caps along with the existing rotary power tube selector. Or maybe I'll just add Dana Hall's VVR and a MV to regulate the power to the PA. Anyway, I'm also currently exploring projects with cheep small signal pentodes in the preamp, so that section of the amp is also still up in the air. But I don't need an FX loop, and I'm thinking a pentode's even-ordered harmonics right before the PI will more than compensate for the lack of a mojo module, and adding a good dose of that pentode sparkle and chime to the mix probably wouldn't hurt either.

Gil...

 

[nomad100hd]

Gil I think I missed the full/half/quarter mod info. I did get my nomad fixed bad relay on the clean channel.

 

[cgil]

Gil I think I missed the full/half/quarter mod info. I did get my nomad fixed bad relay on the clean channel.

Hi Nomad. Good to hear that you finally got the gremlin kicked out of that amp.

The quarter power switch is just so stupidly simple that it's hard to believe nobody actually played with it much before now. Then again, not really when factoring in the strong influence of the penny pinchers. Triode mode only needs the switch and a few wires, versus the additional caps and resistors for the quarter powerder, with or without the extra half-power option, which requires even more resistors. Quarter power mode just lifts the cathodes which thickens the power tube distortion and sounds more like a Single Ended configuration. Half power is just the ticket for gigs when you need to cut some loudness (seems like maybe ~6db) where you don't want any significant change the tone or dynamics of the amp. Pretty impressive, really.

Here's the full scoop.
http://www.el34world.com/Forum/index.php?topic=4401.0
http://www.18watt.com/modules.php?name=Forums&file=viewtopic&t=20058&start=0

And a pic of the one I recently installed in a friend's 18watt homebrew amp. I went a little overkill on the resistor ratings and extra poly caps, but I don't expect to see it again unless the switch fails. :roll:
http://i166.photobucket.com/albums/u103/cgil155/SpitfireQuarterPowerDer.jpg

Gil...

 

[ICR]

Got two beauty RCA grey-glass 6V6GTs over Christmas (parents' attic). Wow these are nice in the Blue Angel.

I had planned on replacing the original 6v6s in the Blue Angel, back when I got it in 1996, but I'm not paying stupid money for tubes that originally sold for like $5. I picked up a few nice 6v6s over the years for Champs, but don't have two nice matching ones. Or at least two of the same age (ie from the same amp).

I'm using RCA 12ax7s for the first two preamp tubes.

 

[cgil]

Sweet! Lucky find, indeed, cuz vintage tubes not only rock, sometimes they seem to last forever, too! I had a weak moment and bought an actual matched quad of RCA 6V6 for seriously stupid money, and I've been sitting on 'em for a rather long time waiting for my Blue Angels resurrection. I did find that a 5751 sounded really sweet for the input tube. They tend to be very quiet and helped tame some of my Blue Angel's nasty hiss issue (serial # 25) with most tubes in that first socket position. And then the amp up and died. :roll: :lol:

But that same old Sylvania GB-5751 is still working (in another amp), and sounding every bit as good as a fresh JAN Phillips 5751 that I recently bought for slightly less at $20 a pop. That Sylvania has already lasted at least 3 times longer than any modern production tube I've ever used; so, if the Phillips 5751's last that long, too, I'd have to say they're still a fairly reasonable bang for the buck.

Gil...

 

[Murphy Slaw]

The Blue Angel is the bomb. I see the used market drying up, as well. People are just keeping them.

I'm keeping mine.

Murph.

 

[cgil]

Yeah! Complex three dimensional power tube grind like that doesn't come along very often. It's definitely a keeper.

Gil...