For this installation if my multi-part instructable, I will be making a chassis out of sheet metal. I have an old Delco radio that I am going to mount the chassis in so I need to make a "box within a box." This will hold the motherboard, the transformers, the tubes etc. Everything needs to fit inside the box and it also has to be wired correctly.
There are a few design considerations when laying out an amplifier chassis, and I prioritized them in this order. First, everything needs to fit inside. This is the most important design feature. I wanted to have the best possible sound from the amp. I wanted to minimize the possibility of noise from the transformer getting into the output signal. I also wanted to keep the tubes from being too close to the exterior of the amp (keeping them safe from being bumped when the amp is getting moved around.)
Sheet of Steel (16 gauge)
Step 1: Gather Your Materials
I am going to make this chassis out of 16 gauge steel. I made sure to get a piece large enough to allow for my chassis to fit on with extra room all the way around.
I am building this amplifier from a kit that I ordered so it makes it easy. If you are sourcing your own parts, this step will be more difficult, however it should not be a big deal. Just make sure that you have everything that you need to fit into the amp before you set out laying out a chassis. You don't want to run into a situation where you have to hack in a tube socket or something. Get it all ready now so that you can plan for all of the screw holes, recesses etc.
Step 2: Lay Out Your Parts on a Table
All of your tube sockets, your transformers, your motherboard, all of the jacks and potentiometers need to get into this small area. Ideally you have enough room where you do not need to compromise any of your design parameters. I however am trying to cram a large amplifier into a box that is a little too small. I prioritized my design parameters so that I can make decisions on layout and compromise my layout as little as possible.
Step 3: Make a Drawing of the Box and How the Chassis Will Fit Inside
I drew out the box first by hand and then in CorelDraw. This allows me to make a digital file of my layout which I can then take to the waterjet. I'll include my file so you can see what it ended up looking like.
I used a set of calipers to measure the sizes of all of my parts. This allows me to make holes for all of the screws, tube sockets, everything. It all should just fit together when it is done.
The dimensions of my panel will be specific to my amplifier and layout, but you could use this method to design one for your enclosure.
Once I have everything spaced out the way I like it, I cut out a template out of cardboard using a laser. Note that the corner bends are fairly easy to do in cardboard, but will be more difficult to do in steel. Fortunately, there is a metal brake at Techshop, so the corners shouldn't be too difficult.
Step 4: Test the Fit.
I used the carboard cutout to check all of my measurements to make sure everything fits the way I like it. I had to move a few things around to get them all to fit inside the confines of the enclosure. I cut all of the bolt holes and everything. It looks like it will come out fairly nice.
After a few minor tweaks, it looks like I'm ready to make the real thing out of steel on the waterjet.
Step 5: Cut It Out on the WaterJet
I used the waterjet at Techshop Detroit to make the chassis out of steel. I used the same exact file that I cut out of cardboard to take to the waterjet.
Step 6: Bend the Corners
I used the metal Brake at Techshop Detroit to bend the corners. This gives me a nice metal box with all of the holes needed to mount all of my components.
At this point, I had a few extra design features that I have to add. Specifically, I made a little panel that is inset inside the chassis to hold my switches. I forgot to take a picture of how I made it, but it is just a little piece of metal that sits inside and holds the switches. I used a spot welder to hold it in place (you can see the welds in the third picture.)
The part will be powder-coated so you will not see the heat marks when it is finished.
Step 7: Assemble the Pieces
I assembled the chassis to test the fit of all of the parts.
I realized at the last minute that I had a few changes to make to the design, so I had to cut out another part on the waterjet, and you can see the two chassis. Not too bad though, considering. I included a side-by-side shot to show the difference between the two. Notice that the first chassis was folded inside-out. Oops. I also made the second try a little taller (.5 in.) This gave me a little more clearance inside the chassis. The output transformer and the rectifier tube swapped places, and I made a few other small changes.
Step 8: Done!
Here is a picture of the amp in it's eventual home.
After quite a bit of head scratching, everything looks great!
Tune in next time as I do final assembly and hopefully make some music!
Also, thanks to all of the messages I've gotten about this 'able. It's been really encouraging. Don't hesitate to ask if you have specific questions.