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 Tele-Meister

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    There be a lot of fairy dust in this industry.

    I’d be hoping for a better noise floor I guess. First one isn’t bad, and my single coils make a lot more noise than the amp, that’s for sure.
     
  2. BobSmith

    BobSmith Tele-Meister

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    Since I’m waiting on another part to get things off the ground, I decided to do a bit more prep work and re-evaluate resistors with my newly found stash. I sorted, measured values and cleaned leads. I found most were just at or slightly beyond spec. I do have fairly good matches so that is good. Given these specs aren’t perfect, I’m hoping it doesn’t throw the project validity off too much.

    Take a look and tell me what you think. These are all A-B, except the obvious MO (not planning to put a carbon comp btw the filter cap) and the 220k which is Stackpole.
     

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  3. King Fan

    King Fan Friend of Leo's Ad Free Member

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    ^^ I like your attention to detail. For me, anything within 10% is good; almost all the old A-Bs I've tried are well within that.

    Much of what I said above is just quoting experts. But the biggest noise improvement I've *personally* experienced was when I subbed MF for the CCs *just in the input chain* of my old 5E3. Huge. I went back and forth on the V1 plate resistors. I ended up back at CC there, but was never sure I could hear the difference, and MF there was probably a little quieter. But the 68ks, the 1Ms, and the V1a 820R -- oh yeah.

    I added a lot more MF in my second 5e3, and tried to leave CC only in the 'Keen' spots. And yes it is quieter than the old one. But not as *much* quieter as when I just "MF'd the inputs...."

    Final evidence: to keep vintage vintage, I left even the inputs as CC in restoring my '67 VibroChamp -- and it's my noisiest amp.
     
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  4. BobSmith

    BobSmith Tele-Meister

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    Back to the build after a little break...

    I sorted all the components, matched values, cleaned (with steel wool) and straightened leads. All PITA jobs. Does anyone have a good way to straighten leads? I have some plastic lined jewelry making pliers that takes out a lot of the kinks. I also found that running a wooden orange stick over the lead on a flat surface also does a good job, but still takes a lot of time. I’m kinda anal with how things look, so maybe I put more time into it than I need.

    I drilled and test fit the board to the chassis. I checked clearances with tube socket leads and jack prongs. Everything really needs to be within a 2 millimeters or it my not fit. That’s my fault for picking turrets and big filter caps.

    I dry fit all the components to the board. Using my first 5e3 as a reference I measured and precut all the lengths of cloth wire. Each one is numbered and indexed on a layout chart. I also used a field diamond sharpener on my wire cutter prior to the cuts in the hope that a cleaner cut of the cloth will prevent fraying.

    Cloth fraying remains an unsolved problem for me. I tried as some had suggested to use a drop of super glue, but I found it really difficult to work with and I’m not sure how to keep it wicking into the wire itself and possibly interfering with the solder joint. I also tried to apply some more wax post-soldering to seal the ends. There were no problems with the wax withstanding operating temperatures. I may try that again.

    Next step is soldering up the board.
     

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  5. JuneauMike

    JuneauMike Friend of Leo's

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    @galaxiex had probably the slickest solution to this. He just fitted a small piece of shrink tubing on the end that he wanted to clean up and then the shrink tube eliminated the fraying. It looked kinda cool too. Look for his Blues Jr. rebuild. It was a very tidy looking finish.

    So I'm assuming the process is to remember to slide the shrink tube onto the wire first, push back the cloth wire and solder the joint. Then slide the tubing where you want it and heat it into place.
     
    Last edited: Jul 29, 2019
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  6. BobSmith

    BobSmith Tele-Meister

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    He actually replied to my post a few months back when I was exploring some options with wax.
    https://www.tdpri.com/threads/working-with-cloth-wire-add-wax.944895/#post-9046722
    It definitely has a clean look to it. Very cool. I actually think my next build is going to go with normal wire for a change and a modern look. But so far I’m getting better results this time...we’ll see how it turn out.

    Here’s the board done up and ready for installation. Now to prepare the chassis...(trannies, ground lugstandoffs and ground bus bar)
    First picture is my original 5e3.
     

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  7. Urshurak776

    Urshurak776 Tele-Holic

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    Bob, after viewing your build threads and looking at your pictures, I went and got all my projects over the last 20 years and just threw everything in the trash.........I'm just not worthy.

    Good Golly you do nice work.

    Ok, gonna ask, since nobody else has....are you Uncle Doug from youtube?
     
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  8. King Fan

    King Fan Friend of Leo's Ad Free Member

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    It is super sano. Bob, how do you like the (all-important) *look* of the yellows vs. the reds, especially on the red board?

    BTW was it in this thread you said Mojotone is still helping you find a good chassis, has a new batch, and sent you another one to try? I'm putting them back on my good guys list!
     
  9. BobSmith

    BobSmith Tele-Meister

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    Haha! I can’t wait to put them side by side to listen, but meanwhile all I can do is look at them. Frankly I think nothing looks better than a filthy old original. That said, I do care of how things look, so it actually bothered me that the yellows had a surprising amount of size variation. And the location of the leads are not centered. They are probably made completely by hand. Perhaps in someone’s oven for all I know.

    I still am waiting for the new Mojotone chassis. They are building me a custom designed head cabinet for my next one and they are shipping it together. I can’t wait to show off what’s coming for the 3rd one. I’ll revive the other chassis thread when the chassis gets here and test it to give a report. As for chassis for the moment I’d keep them on the naughty list.
     
  10. BobSmith

    BobSmith Tele-Meister

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    My dog’s name is not Rusty. :)

    I’m just anal about wiring. I used to work for a big Japanese equipment manufacturer, they made works of art out of thousands of wire. You’d open up a cabinet and your jaw would drop.
     
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  11. King Fan

    King Fan Friend of Leo's Ad Free Member

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    Heh, they do look a bit like the candles we made in arts and crafts when we were kids. I decided I'd put that on the "good thing" list, although I'm not sure yellow Astrons were so 'artisanal.' I was just working with some old Cornell-Dubilier paper caps, and they were 'highly similar' but not identical, especially when it came to the end caps.

    There may be such a thing as 'too tidy' in making repro parts. Ever cut open one of those big blue vintage-sized Sprague Atoms?
     
  12. BobSmith

    BobSmith Tele-Meister

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    I wish I knew what makes a good cap or not, so far I’ve gone on reputation and I’m not sure it’s always well deserved. That’s part of the reason I’m making the iterations of this amp. I would love to report a difference, but I suspect in the end I’ll probably be saying they sound the (disappointingly) the same. Meanwhile, the quest is fun for me.
     
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  13. JuneauMike

    JuneauMike Friend of Leo's

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    Yeah, I'm kinda over cloth coated wire. I like it, but not enough to spend the extra cash on quality stuff. Teflon is my favorite now.
     
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  14. King Fan

    King Fan Friend of Leo's Ad Free Member

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    Back to the fray (so to speak)...

    The many posts about wire seem to end up divided 50:50 between good cloth and good plastic-coated wire of several types. I stick with the cloth especially because (with the good stuff) I like the way it shapes easily, lies down flat, solders easily, and doesn't break. Oh, and looks vintage in Fenders. Here are some ways I've succeeded and occasionally failed to fight the fray.
    1. Bad cloth wire is all over the place; I like the stuff Doug Hoffman sells, pre-tinned but stranded, solders well, shapes well, doesn’t break, no ‘liner’, looks vintage (is essentially the same as vintage) and frays less than most.
    2. The best thing for cutting cloth isn't wirecutters (although the best, sharp, small, name-brand, $$$ diagonal cutters get close). Where fraying is a problem I free up the cloth along the wire after I cut it with snips and then slide the cloth ~¼" out beyond the wire. Then cut *just the cloth* with sharp iris scissors or sewing snips and pull, don't push, the cloth back to leave an exposed end. This method also prevents the 'fat caterpillar' of cloth if you just push it back.
    3. 'Push back' by itself also frays the cloth. Where I don't want to slide the whole jacket along the wire, I may just strip the ends. Sharp, precise wire *strippers* (again, $$$) can strip the cloth pretty neatly. Often just a couple of strands of white thread from the inner core ‘hang out’ when you use good strippers. If so, these can be hand-trimmed with those iris scissors or the ones on your Swiss army penknife. Or, these inner strands also ‘burn back’ pretty neatly. For pale / white wire, you have to be very precise. For this I’ll use a tiny ‘torch’ that turns a pocket lighter into a precise, pointed blue flame.
    4. In either case, a drop of clear lacquer on a chopstick applied to the cloth then prevents future fray and allows any fray that occurs to be finger-shaped back down around the wire.
    5. After that, hey, a tiny amount of fray is vintage correct. :)
     
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  15. BobSmith

    BobSmith Tele-Meister

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    Excellent tips here! Thank you!

    I’d also add that when pushing back the cloth to expose the wire, I pinch the end cloth pretty solidly so that any fat-caterpillar that happens occurs in the middle of the wire rather than the end. I also continue to move it down the wire a couple of inches so there’s no chance of it “creeping back” to fray the end.

    I heard that Hoffman resells Mojotone. I find the Mojotone stuff pretty good.

    Agreed there is something to be said for the look. But my next 5e3 build after this will go to PVC coated wire sold by valvestorm. (18-gauge for filaments and grounds, 22 for the rest). The stranding is already pretinned which is also cool. I used it on on my JTM45 and was very happy with the shape formability, ease of stripping and handling. It’s not as heat resistant as teflon though in a 12 watt amp (or 30 watts for that matter) it’s not an issue at all.
     
  16. BobSmith

    BobSmith Tele-Meister

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    Back from a vacation, the project continues!

    Got the turret board mounted. I’m happy with how it lines up with the tube sockets and the input jacks. The assembly I do with the turrets, Sprague atoms and ground bus requires precision line up of holes within 2-3 mm or things get too close for safety. I think next time I will place the atoms a little further from the tube sockets when I place them. That area gets a bit tight. But when everything is soldered in place it goes nowhere so it’s good even as it is.

    What you don’t see in full on this build, is my grounding scheme. The Mercury PT has a filament center tap (classic tone doesn’t) and the OT has no ground wire but rather self-grounds thru the dog ear mounts (there is no insulating lacquer on this area). So to minimize ground points, I have used one of the mounting bolts of the OT to ground the filament center tap, HT center tap as well as the filter cap ground for power tube section (a black 18 gauge wire comes off the top left cap and goes thru a hole and runs under the board.

    Of course all bolts have some blue locktite to keep secure.
     

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  17. BobSmith

    BobSmith Tele-Meister

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    Power tube wiring complete.

    Extreme closeup shows some difficulty with the cloth, but to just the naked eye, doesn’t look too bad.
     

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  18. BobSmith

    BobSmith Tele-Meister

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    Socket and output transformer wiring complete.

    Note the lack of “obvious” grounding of output jacks. Jacks self-ground to chassis (secured with locking star washer) as does the Mercury OT.
     

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  19. D'tar

    D'tar Friend of Leo's

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    Beautiful!!!
     
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  20. Urshurak776

    Urshurak776 Tele-Holic

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    Awesome! Those blue caps look mighty close to the tube sockets. 2mm indeed!
     
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