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 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
Step 3: Make a Drawing of the Box and How the Chassis Will Fit Inside
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.
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
Step 6: Bend the Corners
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 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!
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.