MIM: 5E3 Style Amp Kit Build Part 2

Published on
January 21, 2021 10:44:34 AM PST January 21, 2021 10:44:34 AM PSTst, January 21, 2021 10:44:34 AM PST
Welcome back to part 2 of our 3 part series on building a Mojotone 5E3 Tweed Deluxe Style Amplifier Kit.  In part 1, we unboxed our kit, installed our major hardware components onto the chassis, and then populated and soldered the fiberboard.  Today, we will continue by mounting the fiberboard into the chassis, setting up our input jacks, and making all the necessary internal solder connections.  So let's get to it!  

Below is a picture of my workbench for the day.  I know I will need some of these tools for certain, others I have a hunch I might need so I just keep them around for when and if the moment comes.  







Alright, now it's time to get our fiberboard mounted in.  First take a look at your chassis and notice the two mounting holes that have been pre-drilled for you (See Image 2A).  Now hold up your fiberboard where you can see the relationship between your fiberboard components and the two pre-drilled mounting holes (Image 2B).






We want to identify a place where we can drill through this board safely in between two components, and then ultimately insert a mounting screw through said hole.  For me, it's looking like the best two areas are going to be those indicated in Image 3A below.  So now, I'm going to make a tiny reference mark on my chassis at the left bottom (closest to me) edge of the fiberboard (see Image 3B).  






Now, let's set aside our component board, grab our backerboard and place it inside the chassis.  Once you have it centered in the chassis and the left bottom (closest to you) corner is line up with your reference mark (Image 4A), hold the backboard firmly in place and flip the chassis on it's side (4B).






You should now be able to use a sharpie, pen, or pencil to make a mark on the backerboard, through the top of the chassis via the mounting holes (See Image 5A).







Now that we know where to drill into our backerboard, let's grab a drill and make it happen.  Once drilled, line up the main component board with the backerboard, and use the holes you've drilled in the backerboard to make the same reference marks on the main board.  And again, once these marks are made, drill the main board.  Now you're ready to use the included 6-32 machine screws and nuts to mount the two fiberboards to the chassis.  Insert through the top of the chassis, line up the backerboard with the screws, and push them through.  Then place your component board on top of the backboard, line the screws up and push them through.  Now apply the nut, and tighten.  In the end, it should look something like this (See Image 6A).  







Now, this being my first time, I did not get my fiberboard perfectly parallel to the sides of the chassis, and this may come back to haunt me later, but I'm going to continue down my path.  And now it's time to set up our input jacks.  If you recall, in the last episode, I mounted my input jacks onto the outside of the chassis (See Image 7A), and we are about to find out why.  So let's orient our outwardly-mounted input jacks in the same way our wiring diagram is oriented (also Image 7A).  






This is going to make our life much easier for a few minutes.  Now all we have to do is follow our wiring diagram and solder in our 1M resistors and any small bus wires that connect jack to jack.  Do not worry about make any connections to/from our fiberboard just yet.  When this is done, you should have something that looks like Image 8A below.  Note:  I've gone ahead and soldered the center and ground lugs of the top two jacks as there are no other external connections that need to be made from here.  







Now let's loosen the nuts on the jacks, and flip them to the inside of the chassis where they belong, making sure our orientation is still correct when we get to the other side.  Once this is done, we need to very thoroughly follow our wiring diagram to make all of the internal connections.  For a more detailed break down here, please refer to the Mojotone 5E3 Tweed Deluxe Style Amplifier Kit Manual, and supplement it with the video below.  






I'm going to start from the right side of the chassis and begin making connections that only have a single component connection point.  In other words, if a wire goes out to another component, and no other connections are coming from that point, I will make the solder connection.  Then I'm going to go back through and focus on the points that have multiple components wired in, so that I only have to make a single clean solder joint.  

Let's take some time to carefully go through our wiring diagrams and make these connections and then meet back here.  Once this is done, things should be looking a little more clean in your chassis.  Perhaps it is starting to look like Image 9A below...







If you're feeling comfortable, let's move on to making certain connections that have multiple components hooked in.  For example, there are a few jumper wires that need to be wired in on our potentiometers, along with some grounding, and a couple of capacitors that need to be soldered in.  There is also a jumper wire between pins 3 and 8 on our 12AY7 that needs to be wired in at the same time as the lead wire from our board is connected to pin 8.  Again, it is best to have a pen or sharpie handy to mark off completed connections on your wiring diagram as you go.  So let's move forward, once again using the above video and our manuals as a guide, and meet back here in a bit.  

Now, I went ahead and wired my output transformer to my output jacks, but did not do anything with the remaining leads on my output transformer.  Currently my chassis looks like the one below in Image 10A.






It's starting to clean up nicely, and now I'm ready to dive into some more complicated connections.  I'm going to start with my green wire, making the heater/filament connections on my tubes.  First I'm going to cut my wire into two equal-length pieces and twist it together (See Image 11A).  Now let's make our connections to pin 4 and 9 on our 12AY7, and leave enough wire lead to connect pin 4 to pin 5 all at once.  Then we continue down the line making these connections to pins 2 and 7 on our power tubes.  At some point, we should look something like Image 11B.  







I'm going to get back in there and keep making connections before I lay my final heater wires over to the lamp.  This is where I'll start making transformer lead connections, and really wiring in all the connections to the power tubes and rectifier.  So let's keep closely following our diagram and meet back here in a bit!    

Alright so I've made what I believe are all the connections on the inside of this amp.  It was a bit of a long process for me as this was my first time.  But I followed the diagram as best I could and I actually feel extremely confident in what I've done here.  Having gone through it now, there are some things I may have done differently to make my life a little easier, such as adding the 1.5k resistors to my power tubes way before I did (this would have made it easier to get my hands in there and make a solid connection).  And really just a number of different connections I would have made in a different order in an effort to essentially work from the bottom up.  All in all, I'm happy with it, and this is where we stop for today.  By now, we should have an amp that is all wired up and ready to be tested with a multimeter.  Maybe it looks something like this one...







In any case, get your meters ready because in our next episode we are going to be testing some crucial points in our amp to make sure the wiring is good.  We will also be installing the speaker into the cabinet, wiring up our speaker harness, installing the amp into the cab, and ripping!!!  See you then!  

Continue To Part 3 >>