More “Mostly” Mojotone 5e3, version 2! (The Yellow Jupiter build)

Discussion in 'Shock Brother's DIY Amps' started by BobSmith, Jun 17, 2019.

  1. BobSmith

    BobSmith TDPRI Member

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    I had a blast building, now playing my last 5e3 from a couple of months ago.
    http://www.tdpri.com/threads/“mostly”-mojotone-5e3-build-here-we-go-again.942893/

    As I was putting away all the extra parts, I looked around and realized I basically bought 2 of everything and Mojotone blessed me with a replacement chassis after the first one suffered from cosmetic chaos from a poor electroplating job, so I figured...let’s do it again!

    I still have all my building templates for placement of board and bus bar (the toughest part of the first build) so this job will be much easier, and may even turn out better!

    Differences for this build...
    The big difference will be the capacitors. I’m using the same Sprague Atom and Sozo, (and therefore I need the triode turret board which is the only one that has the space for Atoms), but this one will use the Jupiter Vintage tone (yellow) instead of the red. Everything else of material significance will be the same (Mercury Magnetics iron, NOS Allen Bradley from my stash. I am using Belton sockets this time, but I doubt that will make a difference.

    I asked a friend who runs a machine shop if I can use their equipment for drilling into the chassis. I’m hoping maybe better tools will keep the chrome finish better than my crappy drill. I think what damaged it was using a center tap which dented and lifted the already weak coating. I don’t plan to center punch this time, rather I will have the chassis in a vise with a x-y table. Sharp bits will help too ;)

    Placement and orientation of everything else will be identical.

    I also picked up a mojotone combo cab with Celestion blue alnico speaker. Mojotone was having a sale...and I caved.

    I can’t wait to get this up and compare it to it’s red twin!

    The parts...and the red twin (for reference)
    379E46A0-1DB9-4D39-9CAD-204587C5846E.jpeg
    The yellow ones... 9C1819AD-2282-4510-94FB-6936442D4888.jpeg
    This is my turret board centering template (slash Amazon box top) D4BE6AEA-E54E-4006-9672-69C9615E4C6C.jpeg
     
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  2. BobSmith

    BobSmith TDPRI Member

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    image.jpg image.jpg image.jpg
     
  3. BobSmith

    BobSmith TDPRI Member

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    Copper donor for bus bar (...on the bottom of picture, in case you were wondering)
    8B921427-BC73-462F-BDCF-93C01D4186B9.jpeg
     
  4. Fluddman

    Fluddman Tele-Meister

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    Watching with interest.

    5e3's are my favourite to build. The mojo tone cab looks great. I'll be interested how the celestion blue sounds - I've often considered putting one in a 5e3 but always ended up using a cheaper Jenson.

    Keep us posted!
     
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  5. SacDAve

    SacDAve Poster Extraordinaire

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    Looks like a fun build. I have a Celestion Blue in one of my 5E3's For lack of better words you get ring like tone out of it that I like. I just hold out on eBay for one for $200. I did a Mojo 6G15 reverb they make really good kits the parts case is great for finding the components and keeping parts organized, but it would nice if you could get the labeling off the case easy when your done.
     
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  6. JuneauMike

    JuneauMike Friend of Leo's

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    Hmm. Why not make it interesting since you are building essentially the same amp again. Like experimenting with a different grounding scheme? Or a 5E3 Tweedle Dee?
     
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  7. BobSmith

    BobSmith TDPRI Member

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    True, it’s really similar. Basically just the coupling caps are different. I’m really stoked about seeing the difference and wiping away or validating myth.

    Funny you should mention the tweedle dee, I really want to build that version too. Since I’m still figuring out the 5e3 tonally (I’m pretty new to tweeds) I intentionally wanted something to solidify my frame of reference. I’ll probably be getting rid of one of these in the end and build the next for variety.

    The grounding scheme I am super happy with. It’s basically the robrob suggested scheme but slightly simpler. His schematic seems to overlook that the output transformer grounds to the chassis and is therefore another possible ground loop point. So I use the output tranny mounting bolt as a ground path for the PT center taps (the Mercury power transformer has a center tab for both the heater filament and high voltage, so no need to bridge the 100 K resistors) and the power section filter caps.

    I could consider an additional grounding improvement by isolating the speaker jacks from the chassis and adding another separate grounding wire to them. Right now, since the output transformer is already grounded to the chassis, and has just the 8 ohm output lead on the secondary I have the output jacks going to ground thru their own chassis mount. Seems to work well.
     
  8. JuneauMike

    JuneauMike Friend of Leo's

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    1. The only reason for guitar players to care about "grounding schemes" is noise. If its not a problem, move on.
    2. You have a 5e3 already, so you won't figure it out any better than by playing the stock version of it now. The Tweedle Dee would just be a FYI.
     
  9. BobSmith

    BobSmith TDPRI Member

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    Mojotone cab is nice. I got it mostly because of the Memorial Day sale, it seemed like a bargain I couldn’t pass up. But frankly, the last cab I bought was even better. It was custom made (to my specs for head and matching cab) by a guy in Aransas Pass, Texas. He sells by a few names on the internet: Fullerton Classics and Masterbuilt Tweeds. (Has a Fendery ring to it) You can find his stuff on eBay or Reverb. Comparably priced.

    I’ve already run the alnico blue thru my other 5e3. What can I say, but Glorious!
     
  10. Fluddman

    Fluddman Tele-Meister

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    Cheers Bob. I may just give a blue a go in one of my 5e3s. ;)
     
  11. Urshurak776

    Urshurak776 Tele-Holic

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    Your last build is the neatest wired 5E3 I have ever seen. Looking forward to this one and hearing your thoughts on the differences.
     
  12. JuneauMike

    JuneauMike Friend of Leo's

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    Yes, but Robrob's bus bar grounding scheme isn't the only one out there.

    http://www.valvewizard.co.uk/Grounding.pdf

    Experiment. Live a little. Then report your findings. ;)
    Ha.
     
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  13. BobSmith

    BobSmith TDPRI Member

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    Ok, so I was HOPING I could do things a little better this time around. Turns out I was wrong.

    I was really upset about the poor electroplating job mojotone did on the chassis. All the holes I drilled for mounting the turret board and grounds developed an ever expanding peeling of the coating. I thought part of the problem was center punching and using crappy hand tools.

    A friend of mine runs a machine shop so I brought my chassis to his shop to use some better tools. I center drilled instead of center punch (hoping to avoid bending the metal), and used cutting fluid with the drill press. However the result was unchanged. Lots of peeling! That makes 2 in a row. Very disappointing....

    Is there a better chassis that takes drilling a little better?
     

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  14. Uncle Daddy

    Uncle Daddy Tele-Holic

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    Mojotone now has a warning on the website about modifying the chassis. I used a TAD for my last build, but the mirror polishing isn't as good.
     
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  15. King Fan

    King Fan Friend of Leo's Ad Free Member

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    That is a *bad* chassis. It's a shame. I got my 5e3 chassis from Mojo just last year and it stood up great to drilling, punching, etc. But as @Uncle Daddy points out, the Mojo website now says: "Modifying or drilling this chassis will compromise the chrome finish. Flaking or peeling of the chrome may occur. We cannot accept returns for a modified chrome chassis." They've obviously switched plating shops -- and don't care.

    The problem is I don't recall a build where I didn't 'modify or drill' the chassis. I'd write a bad review on the Mojo site and see if they post it. Was the warning there when you bought yours? They are *not* inexpensive.

    One problem I picture in looking for alternatives is that many online shops just resell Mojo stuff. Then too, when I shopped around last year, I did find a few less expensive offerings that had obviously inferior chrome -- tiny air bubbles, subsurface scoring, etc.

    I wonder how Weber does? I wonder who else makes a *good* 5e3 chassis?

    I'll probably still recommend Mojo's galvaneal chassis -- eg, the PR. But I'm moving Mojo down on my *good guys* list.
     
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  16. BobSmith

    BobSmith TDPRI Member

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    I’m not sure if the warning was there at the time I bought it. It may have been.
    I will say that their customer service in dealing with it and other issues has been very good. They offered me the second chassis free of charge which was nice. When I’ve had a mistake in orders, they have been prompt and helpful in getting me the right things. That goes a long way for me.

    They probably did get a bad batch of electroplating. They seem to be aware of the issue given the notation. It’s anyone’s guess when or if it will be corrected. In the meantime, unless you like or don’t care about early relic’ing people may want to avoid the chassis if planning modification.

    From a manufacturing point of view, one of the engineers at the shop said these things can happen and so ideally it’s best to electroplated after holes punched which is what mojotone’s supplier clearly does, and then we come along and screw it up... ;)
     
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  17. BobSmith

    BobSmith TDPRI Member

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    Today I drilled and test mounted the turret board and bus bar standoffs. Overall happy with the results, but I think my first amp’s placement was slightly better. (Again reminded about the tiny fit!). There is plenty of clearance for tube socket leads, but the input jacks are closer to the board. Still away from the turret, but could in theory touch a lead if someone is not careful when poking around inside. I plan to route the wires from the base of the turret away from the jack to minimize this further.
     

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  18. BobSmith

    BobSmith TDPRI Member

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    I sorted thru my resistors and found enough NOS resistors to do the whole amp. I measured and selected the best and closest matching resistors. Most of the are now out of spec, but of the ones I picked only a few were actually worse than expected tolerance of 5%. Then I straightened and cleaned up the leads with steel wool (these are the ones in baggies below my original supply).

    The mojotone kit ones were more or less right on the money for spec. (I have a ton of the mojotone ones of course)

    The ones I have here are Allen Bradley to my belief with the exception of the 220k (which I know to be stackpole).

    I’m thinking of using these, just because I can. I’m curious what other folks would do. Use them, or perhaps sell the lot on eBay? Tempting. I have about 2 or 3 times more of these around.

    P.S. I don’t plan to use the 22k one which is used on the filter cap. I think a metal oxide would be better, that’s why it’s there.
     

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    Last edited: Jun 30, 2019
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  19. King Fan

    King Fan Friend of Leo's Ad Free Member

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    Where I wanted CCs I’d go with the A-Bs for sure. Nice collection!

    What about the 4.7k?
     
    Last edited: Jul 1, 2019
  20. FenderLover

    FenderLover Friend of Leo's

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    Ted Weber got sick of dealing with plating issues, so he went to polished stainless. Can't beat it.

    It's not Mojo's fault, they don't do the plating, but they have to live with the quality problems and bad rep because of it. Kind of a shame, really. Then again, if they are still using the same plating vendor, serves them right.
     
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