Article by Logan Tabor -- Dec. 18th, 2020
Welcome back to another episode of our Fix It Friday series. Today, we’ll be diving into one of our British Style Amp Kits, the NC3015. This is a 15 Watt EL84 amp, and it is available as either a head or a combo on our website. The amp I’m building today will actually be going to one of our artists, Hanan Rubinstein. Hanan will be using this amp in his studio to broaden his selection of tones for any given project.
I’m particularly excited about this one, as it will be my first British Style kit build. Another high point here is this: If you’ve been following along with our Tweed Style kit builds, you’re aware that those Tweed chassis are very narrow and can be tricky to work in at times. This chassis is much wider and should feel luxurious in comparison.
Before we dive in, let’s take a look at what you’ll need in order to join in today:
Mojotone British Style NC3015 Head Amp Kit
Mojotone Chassis Stand
We’ll be breaking this project up into three different articles. Today being the first of those three, we’ll start by getting all of our hardware installed in the chassis. This hardware will include our transformers, tube sockets, can cap, jacks, pots, switches, metal standoffs for the turret board, grommets, fuse holder, light assembly, and AC inlet.
I like to start by installing those components who lie (or whose mounting hardware lies) closest to the floor of the chassis. In this case, we’ll start with our transformers. But before we get carried away here, it’s important to acquaint ourselves with the wiring diagram. Right now we’re looking for two big things. Take a look at the diagram below (Image 1A) and note that the diagram shows the front panel of the amp (the side with all of the potentiometers) being farthest away from us. I’ve also circled the points on the diagram that indicate the wire routing holes for the output transformer wires. These holes are where we’ll insert our rubber grommets; we’ll also need to be mindful of which wires go through which holes as we proceed…
Now that we are oriented properly and have our bearings straight, let’s go! I’m going to start by inserting my rubber grommets into the holes indicated in the above image. Next, being mindful of which wires go through which holes, I will router the output transformer wires through the routing holes from the underside of the chassis to the inside. Next, I’ll insert my 8-32 screws into their mounting holes from the underside to the inside of the chassis. Using one hand to hold the transformer and screws in place, I’ll grab my 8-32 keps nuts and hand-tighten them from the inside of the chassis.
After hand-tightening both nuts onto their respective screws, it’s likely easiest to turn the chassis on its side and use a screwdriver and adjustable wrench to finish tightening everything down. When you’re done, the inside of your chassis should look similar to that in Image 2A below…
Now let’s move on to the power transformer, the big guy! Same basic concept really; except the power transformer has built-in mounting threads already. Take a look at the wiring diagram again to make sure you’re familiar with the wiring orientation before inserting the power transformer from the underside of the chassis to the inside of the chassis. Once you’re in place, start hand-tightening your remaining 8-32 keps nuts onto the mounting threads. Then you can use an adjustable wrench, or nut driver, to finish tightening. Now you should look like the chassis in Image 3A below…
Now I’m going to mount my can capacitor. So let’s locate the can cap and its mounting ring. You’ll need to loosen the mounting ring all the way to slide it over the can cap. You’ll notice that the side of the can cap closest to the solder lugs has a groove or indention in it. You’ll want to make sure the mounting ring sinks into that groove before tightening the mounting ring back down. Once your ring is tightened back down around the cap, here’s how you should look (Image 4A).
It’s important to note here, that you will likely need to make adjustments to the orientation of the cap within the mounting ring. We want the ground pin of the cap to be closest to us once it is installed, so we may have to spin the cap inside the mounting ring so that we are lined up in two ways: 1) the mounting ring holes are lined up with the chassis mounting holes and 2) the ground lug of the can cap is closest to us while we’re working. When you’ve got it situated properly, use your 6-32 screws and keps nuts to fasten everything down, and then you should look like Image 5A below....
Now we’re going to move on to installing our tube sockets. These are all 9-pin sockets so installation will be uniform throughout. First, look at your diagram and notice the orientation of the pin number on the tube sockets. Then look at your tube sockets and make sure you’re aligning them with that of the diagram prior to installing them. These will need to come up through the underside of the chassis into the inside as well. Now you know what to do: get the sockets in place and, using your 4-40 screws and keps nuts, start hand-tightening them down. Once they’ve all been hand-tightened, go back and finish tightening with your tools. Then you should have something that looks like Image 6A below…
I’m going to move on to my metal standoffs for mounting the turret board. There are four of these pieces that need to be installed, and they need to go in the remaining four holes in the floor of the chassis (you’ll see them highlighted in Image 7A below). The inserts themselves have internal threads that will match up with four of your remaining 4-40 screws. Just insert the screws from the underside of the chassis to the inside, and then hand-tighten the metal standoffs onto them.
Now it’s time to move on to mounting our front panel and back panel hardware. We’re going to begin with the front panel. Keep in mind, we’ll need to make sure our faceplate is installed along with these components, so while we’re installing our input jacks, we’ll need to be getting faceplate mounted as well.
Beginning with the four input jacks in the image below, I like to remove the nuts from all of my jacks right away, and leave the small black washer on the jack. Then, with the faceplate properly aligned, insert the jacks one at a time from the inside of the chassis through to the outside of the chassis and tighten down the nuts from the outside. Make sure the solder lugs on all of your jacks are running parallel to the chassis (Image 8A).
You can now go back and use your adjustable wrench to tighten the nuts a little more, but be careful not to scratch the faceplate in the process, and don’t over-tighten the nuts as you risk causing cosmetic damage to them as well.
Now we’ll move on to the pots on the front panel. Consult your wiring diagram to make sure the pots of the proper value are going into the right positions. Here again, remove the nuts and the washers from the pots, but in this case we’re going to leave the lock washers (knurled) on the pots when we put them into place. Insert the pots from the inside of the chassis through to the outside, slide the washer over the threads from the outside, and hand-tighten the nut from the outside. You can then go back and use your adjustable wrench to finish tightening. Again, be wary of faceplate damage and over-tightening. You should now have something that resembles Image 9A below…
Alright, the rest of the hardware for the front and back panels of the amp will follow the same basic principles and procedures as those for the jacks and pots. In light of that, we are going to lump the rest of this hardware together and knock it out in one fell swoop. One thing we’ll definitely want to remember in all this is to make sure we install the red backplate while installing the rear panel hardware...definitely don’t want to forget that!
In whatever order you choose, install your standby switch, power switch, light assembly, fuse holder, AC inlet, impedance selector switch, and rear panel speaker jacks. We’ll meet back here soon and we should all have something resembling Image 10A below…
Well folks, we’ve arrived at the end of today’s walk through, but we’ll be back soon with part 2 which will include stuffing the turret board and wiring up the amp; i.e. the fun stuff! This thing is gonna sound absolutely awesome when we’re done, and you won’t want to miss it so stay tuned.