Building a Mojotone NC3015 Amp Kit: Part 2

Written by
Logan Tabor
Published on
January 22, 2021 at 12:19:20 PM PST January 22, 2021 at 12:19:20 PM PSTnd, January 22, 2021 at 12:19:20 PM PST

Welcome back! Today, we’ll be picking up where we left off on our NC3015 amp kit build. Last time, we were able to get all the hardware installed, so today we’ll be installing and stuffing the turret board, as well as wiring everything up. This is really the fun part, and I’m definitely looking forward to it so I hope you are too.  

One thing we didn’t touch on last week was the installation of our ground tabs, so we’ll talk about that now. There are three ground tabs that come with the NC3015 kit and they’ll allow us to have reliable ground connections located in strategic places within our chassis. You can see these ground tabs on your wiring diagram as well as in Image 1A below.  

As you can see, you’ll need to loosen a few mounting screws from other pieces of hardware to get these ground tabs situated, but it should just take a couple seconds and then we’ll be ready to embark.

Here is a quick list of tools you’ll need for today:

As we’re preparing to move on to the next step in the build, we need to consider a few things. If you’ll notice, your turret board has the longer end of the turrets sticking out of the top. However, there are also little metal eyelets on the bottom side of the board. This means you have a choice in how to wire the leads coming off of the board: you can either stuff the components up top, and solder all of your leads from the bottom side, or you can put everything up top. For this build, I’m choosing to do everything up top, which means I can go ahead and mount the board in the chassis before I stuff it.  

As I mentioned, my first step is going to be to mount the board in the chassis. We’ve already mounted our metal inserts in the chassis, so all we need to do now is make sure our turret board is oriented properly and then use our remaining 4-40 screws to fasten the board down. Refer to your wiring diagram for proper turret board orientation and then get it mounted. Once you’re done, you should be looking like the chassis in Image 2A below…

Now we’re ready to stuff the turret board with components. One thing I like to do with these turrets boards is get all of my jumper wires in place first before stuffing all of the capacitors and resistors. Jumper wires are illustrated on your wiring diagram as red, silver, and black wires that connect two turrets on the board. Take a look at Image 3A for a few highlighted examples of jumper wires…

We can use the red and black PVC-coated wire that came with our kit to make these jumper connections. We’ll simply need to measure out the length of wire needed for each jumper, strip a bit of insulation off of each end, bend the wire ends down at a 90 degree angle, and insert them in the corresponding turrets. Or, as an alternative, you could strip more insulation off the ends of the jumpers than you normally would, and then wrap the leads around the middle of the turrets as opposed to placing the leads into the turret holes. Once you’re done with the red jumpers, you should be looking similar to Image 4A below…

Then you can finish up the black and silver jumpers and you’ll be ready to move on. The next step is to stuff all of our capacitors and resistors in the board. This is a part that will require heavy use of our wiring diagrams. It’s basically like putting a puzzle together, so just follow the diagram, locate the proper value of each part and put it where it needs to go. One big thing to watch out for is this: on this board, we have 5 polarized capacitors. This means they have to have their negative and positive ends facing in the right direction in order to work properly. Take a look at Image 5A below and notice the highlighted capacitors…

Those circled in red are the ones you’ll need to watch out for. As you move forward, just reference your diagram for proper orientation and you should be in good shape. Alright, let’s get to it! Take your time and follow the diagram, and let’s meet back when our boards look like the board in Image 6A below…

Now we have our boards stuffed with the necessary components, but before we start wiring everything up, there’s another preparatory step we need to take. If you look at your wiring diagram, you’ll notice that many of your potentiometers, jacks, tube sockets, etc., have a component or jumper wire running between solder points. Now would be a good time to go ahead and get these components in place so that when we move on to the final wiring, there will be far fewer “surprises.”  

A good way to go about this is to identify one of these components or jumper wires, and wrap their leads through and around whatever lug they need to connect with. Then you can use your needle nose pliers to pinch the leads down and hold the component in place until it’s time to solder.  

Let’s spend some time with our wiring diagrams, pay close attention, and get all of these parts into place. We’ll meet back once our chassis looks similar to the one in Image 7A below…

Okay, this seems like the right time to embark on a magical journey called “wiring everything up!” This is going to require patience and focus, among many other qualities. Here are some things to keep in mind throughout this process:

1) Make sure ALL components are installed in any given solder point before soldering (we only want to solder one time per joint if we can help it).

2) Try to route your wires as close to the chassis as possible to avoid clutter and to make future maintenance/repair work easier.

3) Your wiring diagram uses different color wire for different connections; follow this color coding as best you can so your wiring diagram will be as relevant as possible next time you open up the amp.

4) Take as much time as you need and try to have fun; you’re giving life to supreme tone here!

Alright let’s dive in. A nice tip here is to go ahead and look at the potentiometers on your wiring diagram. You should notice that two of them need to have a bus wire running from one of their lugs to their metal casing. You'll definitely want to go ahead and knock this out before you start wiring up the pots, that way no wires are in the way when you go to do it. It is also good to use a flathead screw driver to scrape off some of the coating that's on the pot's metal casing; this will help the solder adhere more readily.

After that, I like to continue to the soldering phase by identifying those solder points on my wiring diagram which do NOT need to have a lead running out to other components in the circuit. These points can go ahead and be soldered without having to measure and route wires. Once I’ve got those lead-less connection points soldered in, THEN I’ll move on to measuring and routing lead wires for the rest of the circuit.  

At this point, I'll begin working with my power transformer leads as well as my output transformer leads. This not only helps clear up your work area and get those long wires out of the way, but a lot of your transformer connections are single component connections which make for a nice easy start.

Another thing I like to do is keep my wiring diagram in front of me and use a pen or pencil to mark off connection points as I solder them. This helps me stay organized and acts as a quality control method as well.

Well folks, this is one of those parts where we pretty much have to set you loose with your wiring diagram and meet back when you feel like you’ve got everything in place. So let’s take out time and get all of our internal connections soldered in! See you back here when you’re looking like Image 8A below…

Well that was really something special. In retrospect, I think next time I would prefer attaching my lead wires to the eyelets on the bottom of the turret board prior to even installing the board within the chassis. Some of the turrets which had more components stuffed into them became difficult to get my leads into which made for a little more work; going with leads on the bottom would also probably make for a cleaner look altogether.  

Hopefully everyone was able to make it to this point, which is a really great stopping point! Stay tuned for Part 3 wherein we'll clean up all of our solder joints and begin testing voltages throughout the amp to see if everything is looking good. Thanks again and we'll see you next time!