Lots of beginner questions for a Mojo 18watt TMB build.

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revjamie
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Lots of beginner questions for a Mojo 18watt TMB build.

Post by revjamie »

Hey Everyone,
I decided to build a mojo 18 watt TMB kit and have been reading the forum. Lots of great information here. Even read the full "What Every Newcomer Should Know..." sticky post.

I'm pretty new to amp building. The only project I've done so far is replace a bad PCB in a 74 50 watt Marshall with a board and parts from Valvestorm. Turned out pretty well.

I'm having some issues with the Mojo kit. Or better yet, things I don't understand and was hoping maybe people that have built this mojo kit could offer some insight.

#1 The kit didn't come with any ground lugs, but rather two terminal strips. That's fine, but the don't fit on the power transformer bolts. I've seen some photos from people who have done this kits and it looked like they were able to get the terminal strip onto that bolt. You can see their photo here:
Image

I can get the strip to fit on the bold that holds down the capacitors like the photo below.
Image
So I'm wondering, should I drill out the hole in the terminal strip? Or just go with it on the capacitor bolt?

#2 The kit didn't come with any bus wire. That seems kinda weird. I guess they want you to use the green wire maybe?

#3 I've never dealt with cloth covered wire before. It kinda seems like a pain in the ass compared to plastic covered wire. Is there any reason I should use the cloth covered wire instead of plastic?

#4 I saw a cool photo of the 36 watt on this site, and all the solder connections were covered with heat shrink. Looked killer, is there any real benefit to that? I seem to see a lot of posts where people are having issues with hum, is the heat shrink to help with that maybe?
Image

#5 I noticed a lot of builds where people posted photos here they are wrapping the wire around the turrets and doing the same with the caps and resistors. Is there a reason for doing that instead of sticking them inside the turret? Maybe easier access to tweak things later?
Putting the caps, resistors in the turret hole is what I did on my 50 watt board replacement. Actually I ran the wire underneath the board into the turret holes following a Metro Amp step by step.

I appreciate any advice or suggestions anyone could offer.

Thanks,
Jamie
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JMPGuitars
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Re: Lots of beginner questions for a Mojo 18watt TMB build.

Post by JMPGuitars »

Hi Jamie,

Welcome to the site! I'm happy that you're asking these questions before building. :)

#1: Ground lugs or terminal strips is maybe a matter of opinion, personally I prefer ground lugs. However, never use anything for ground lugs that has another purpose. That means, transformer bolts, cap bolts, etc... shouldn't be used for grounds. Drill new holes for grounds. While we're on the subject, you might want to research ground schemes before you build your amp. This is not the same amp build, but you can follow the same philosophy: files/JMPGuitars_18_Watt_Lite_2b_Layout.pdf - one ground point close to the input jack covers the input jack, pots, and preamp. Another star ground covers the filter caps, output, and center taps, etc... and the IEC ground ALWAYS gets its own ground point.

#2: I don't know about that kit, I'm not a big fan of it (you may notice a lot of posts on this site with people discussing issues with it). That doesn't mean you won't get a great amp out of it, but plan ahead to improve the kit, and you'll get a better amp. If you want bus wire, buy bus wire and use it, as long as it fits without conflict.

#3: They probably use it because it's "vintagey" - it's not too difficult to work with; try pulling the cloth back instead of trying to strip it.

#4: Thanks, that's my amp/build. :) I'm sometimes obsessed with heat shrink. Besides looking awesome, it helps ensure that there's no stray wires or unwanted contact doing things they shouldn't be. In some spots, like the PTP FX Loop, it wasn't optional.

#5: Generally speaking, that creates a better physical connection. Either way works, but if you get the hook around, and you have good soldering skills, you can always see the quality of the solder joint. With the solder joint in the hole, you're running on a lot of faith. Which is usually okay if your skills are good. If at some point something overheats, the wire in the hole's connection could lift and come loose, but a hooked wire will most likely stay in place.

This (#5) is actually why it's also a good idea to wrap wire through solder lugs and bend it back to create a physical connection before soldering.

Thanks,
Josh
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revjamie
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Re: Lots of beginner questions for a Mojo 18watt TMB build.

Post by revjamie »

Hey Josh, thanks for all the great info!

#1 That makes sense about the ground lugs. I’ll drill holes for my lugs and follow the ideas in the 2b Lite PDF.

#2 I kinda figured about the kit. I thought it’d be a good jumping off point and get me all the stuff I need to start out with. Then I can swap out parts as I see fit.

#3 This is BRILLIANT! That was my issue with the cloth. It seemed like a pain in the ass to strip and get it to not have a bunch of hanging threads and stuff. Just clipping it and pushing it back makes a lot of sense. I’ll give that a shot.

#4 Congratulations on building that amp. The insides are beautiful! I like the heat shrink idea a lot.

#5 Makes sense about the connections. Hooking the wire around the turrets. Also makes sense that you won’t need to pop the board off if you need to make some changes and stuff.

Thanks again for the tips. Here we go!
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Wnively321
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Re: Lots of beginner questions for a Mojo 18watt TMB build.

Post by Wnively321 »

revjamie
The guys on this forum are awesome and have helped me a lot

It looks like you are building the same kit I did. Mine has so far been 1 huge noise problem. This is the 3rd tube amp I’ve built ,the 2 prior were fender clones with no issues what so ever.

In the past I have built several 1176 clone kits and many 500 series preamps ,compressors etc....
I have never had 1 failure
The good people on this forum have been more helpful than the seller of the kit who promises tech support and btw I haven’t heard from their tech support yet
My advice would be to send it back and buy from one of the sellers recommended by this forum.
I wish that’s what I would have done
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Wnively321
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Re: Lots of beginner questions for a Mojo 18watt TMB build.

Post by Wnively321 »

My apologies , looks like your building the TMB kit . I built the tremolo kit.
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tom_k
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Re: Lots of beginner questions for a Mojo 18watt TMB build.

Post by tom_k »

revjamie,

I just finished building that kit...
My kit came with all the buss wire needed. I like the cloth wire for everything except the heater circuit, That stuff is a bitch to work with when twisted.
My kit came with a lot of the green wire, a bunch of yellow and a bit of white.

I had one missed ground connection, when fixed she is very quite and sounds good.
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revjamie
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Re: Lots of beginner questions for a Mojo 18watt TMB build.

Post by revjamie »

I know this kit isn't the best. But it was pretty cheap, and I wanted something that I knew if i totally **** it up, I wouldn't feel so bad. Kind of a dry run for doing a really great one.
I'm thinking once I do this, I'll have a better feel for the build, all the parts, how they go together etc.
Once I'm done with this one and if it's a success, I'll probably piece together a kit picking out all the parts on my own. Maybe give this one to my nephew or something.
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