Building a combo Cabinet

Getting started
Every so often someone asks advice about building cabinets so i thought seeing that I have built a quite a few that I would share the methods used in the build completed this week. This is by no means the entire process but hopefully will be enough to fill in some of the blanks for a first time builder.

This particular cab is a combo for a 5E3 [late 50's Fender deluxe] clone built by Jim Nickelson at Little Dawg Amps, California USA. . The circuit is housed in a Mojotone chrome reproduction chassis. At the time of starting the project the chassis build had just been ordered with a lead time of 3-4 weeks.You should be very clear on the chassis and speaker dimensions before beginning if the chassis is not in your workshop. If it is your first I would wait for the speaker and chassis to arrive and content yourself with completing a working drawing of the project.

I have built this project before so i know the cab size. It it fits the Jensen 12" Neo speaker I want to use and the chassis. The design is based on the narrow panel tweed deluxe cab dimensions. You can get the measurements for most fender cabs from the fender amp field guide, a great resource if you are a fender nut like me. The weber speaker site has many repro cab sizes in their amp kit section as well. If you base your build on a tried and true design it has to sound good and be able to fit the various bits in right?

Lets start with the chassis first - both front and rear views -
Mojotone Tweed Deluxe chrome steel repro chassis - very nice.
The mount points are visible either side on the front
A nice new set of JJ 6v6's, a 12Ax7, 12AY7 and a NOS RCA 5Y3GT came in the box - mmm my favorite 5E3 set
According Jim you can mix and match the valves in the 5E3. Use a 5Y3Gt or Gz34 rectifier valve with 6V6 or 6L6 output valves. The 5Y3Gt, 6V6 combo will give the saggy warm tone the 5E3 is famous for. The Gz34, 6L6 combo will give more headroom and a clearer chimey tone. You can also experiment with different pre-amp valves eg: substitute the 12AY7 with another 12AX7 for more gain.
I am lazy and rely on some great tools I have in my small but nicely equipped workshop. You could do it with a circular saw, jigsaw and hand held router plus various screw drivers, hammers, chisels, squares etc. The dovetails in this job are cut with a Leigh jig [expensive] and a router. There are cheap dovetail jigs around if you want to rout them. You could do it the old fashioned way and use a gents saw and chisel. You will need patience and skill, while using the Leigh jig is total a no brainer :) Some of the cheap dovetail jigs work well but can be tricky to use.

I have used 300x19mm Porta panels bought from my local bunnies. I like these as they are accurately machined and this does save time as well as make an accurate job easier to achieve. As they are a panel of 50x19's laminated together Porta panel is reasonably stable but are not cheap.

As the cab is 220mm deep there is enough in the 290mm width to cut the fascia panels, fascia infill's and 19mmx19mm rear panel mount cleats.
There is another product called Knotties and they are similar but in Brazilian pine which is a great colour but the panels tend to split and cup indicating a high moisture content.

If you spend some time picking over a pack of 300x19 DAR pine at your local timber yard you will walk away with a lot more cash left in your wallet. Do expect to have to trim the boards up as they won't be too accurate. Also watch out for badly cupped boards and loose knots.

Front and rear baffles are made from 12mm British Standard Marine ply which is a pretty nice ply at around $90 a sheet [1200x2400] its a bargain. Don't use the pine ply crap they sell at bunnies.

The Grill is Oxblood yellow stripe from Evatco as was the jensen neo speaker and the "no animal died" handle.
Nuts bolts and screws are pretty much all stainless steel.

Construction Methods
Through dovetails are strong and require no braces, fillets nails etc to support the corner joints. The rear panel mount support cleats are screwed and glued. The fascia panels are simply clamped and glued on to the front of the carcass. I then clean up the edges with a plane so they are flush.

The front baffle is cut from 12mm BSM ply and the speaker port is cut with a router. 3/16" Teenuts are mounted around the speaker port on the front surface. I use a 20mm slice of 3mm MDF glued around the front edge of the baffle to lift the grill of the baffle a little. I have heard it can slap onto the baffle if there is no space between. I have never heard it happen but apparently it doesn't sound so good. Before the grill is stretched on I paint the front of the baffle in matte black. The grill is stapled along one edge then stretched over the opposite edge. Once its down nice and tight the sides are stapled as well. The baffle is simply screwed from inside the cab directly into the front fascia panels.

Nothing more complicated than making a few nice square, straight cuts and measuring accurately and often. If you look at the pics you will find it a basic and straight forward build. This cab will easily support my fat arse for a nights playing. It is easy on the back with the finished job including speaker and chassis weighing around 11Kg.

Protect the surfaces carefully a crucial part of the job is the way it looks when finished. Right from the very first cut you should be watching for any little thing that can mar the surface of the timber. A stray nail, screw, lump of dried glue or whatever can make ugly scars on the surface that you will notice when you start surface prep. Some dings can be carefully steamed out but others will remain stubbornly until leveled with crack fill.
Always lay your timber / cab onto a towel, routing mat or similar soft surface. A careful approach will avoid the painful process of masking scars.

The build

Laid out below are pics and explanatory notes showing some of the major points of construction.
The carcass after glue-up
After you have machined up the boards, cut the dovetails and glued it up nice and square it should look something like the above
The basics done
After the carcass is out of clamps the front fascia panels and and infill cleats are glued directly onto the front of the carcass. Shown above with the baffle in place. The rear panel support cleats are glued and screwed down and at this point the various holes need to be marked out and cut. eg. Handle support screw holes, badge mount holes and panel cutout. It is way easier to mark these out with the edges square than after you have machined in the round over.
Detail of fascia panels
Clearly visible is the method used to attach the front panels. No dowels, nails or screws are required.
Rear panel supports
The rear panel support cleats glued and screwed in place. I allow a little machining tolerance here to take account of sanding. I like the back panels to be slightly below the cab edge rather than sitting proud.The ply being 12mm I allow 13mm. The speaker baffle is screwed onto the fascia panels with SS # 8 wood screws in cups.
Control panel cutout
The control panel cutout is measured and carefully marked and cut using a jigsaw. The handle support screw holes and any other holes, marking out etc should be completed prior to round over. It is tricky measuring accurately from rounded edges
Make certain your marking lines are clearly visible. I use a 1mm felt tip marker
With straight sided off cuts screwed tightly to the cab and lined up carefully to the lines, it is time to clean up the cut out with a spiral upcut bit.
There it is - this spiral bit certainly cuts a nice smooth face. Note the protective piece clamped the front left
that protects from tearout where the router exits
Test fit the chassis, carefully center it and get the front rear to rear position correct and mark the holes for the mount bolts.
carefully extend the center over the edges to the top as I am going to cut the holes from the top with a drill press to ensure they are perpendicular. Any chip out will be underneath and not visible. To be doubly sure I will clamp material under the hole and use a brad point bit. This will minimise chipping around the exit hole.
The nifty little incra bend rule that makes extending lines around corners easy.
Everything looks right with the chassis bolted in, and the rear panels fitted it looks like I am all set for roundover. Once everything is flush rear and front, the dovetails are flush and all holes and marking out are complete it's time to do the roundover's.

I use a table mounted router with a 3/4" roundover bit. It could be done with a hand held router or a plane, rasps and sandpaper. Completing the roundover's signifies the end of building and the beginning of the finishing phase.

Prior to sanding fill all voids with a decent woodfiller. Alow a few hours to dry and start sanding with 120 or 180 grit and go through to 240 or 320. Be sure not to miss any grits as each successive grit will cut away the scratches left by the previous grit leaving its own smaller scratches. By the end of the process the scratches wont be visbile to even the keenest eye. I use a Makita 1/3 orbital sander on the faces and use my fingers to do the edges and corners. Be sure to steam out any dings and scratches as you go. I have knocked off the corners to enable the fitting of protective steel corners.

Surface Perparation
If you are tolexing surface prep is not so critical. Roughly fill the gaps and holes with Timbermate water base wood filler, A quick once over with 180 or 240 grit paper and you are ready for glue and tolex.

Varnishes, lacquers or french polish
You will need a finely prepared surface with all voids filled. Sand to no more than 400 grit with 240 grit being most common. The most challenging finish of all but nothing beats that mirror gloss. The road to a perfect finish using this method is long and tortuous. Recomended for studio or loungeroom.

Quick and dirty
A couple quick brushed coats of semi matt clear, a brisk rub down with coarse steel wool and an application of furniture wax. Looks surprising good for the amount of work involved

Oil and Wax
This job will be done using Danish oil and wax. Sand from 180 grade and finish at 1500. Don't don't skip any grades grits as you will end up with visible scratches. Fiinish up by polishing with the rear face of any grade wet n dry paper. You will be surprised at how much of a shine thast will put on the pine. It is critical that you carefully proceed through all of the available grades of paper. Application of the DO [Danish Oil] is a no brainer. Other oils can be used such as boiled linseed oil. tung. oil or other commercially produced products. Danish oil is easily applied and cheaply made using recipes available on the wwww. I like Cabots DO as it is so easy to apply and makes a really nice job. Typically the surface is carefully sanded to around 1500 grit and buffed with the rear side of a piece of wet n dry paper to bring up the sheen of the polished wood.

The finished surface after the application of Danish oil

After you have finished with sandpaper to the point you can see a definite shine, give the surface a rough going over with Danish Oil on a rag. Don't be afraid to slap it on. Give it a minute or two and wipe off the residue with a dry, clean, lint free rag. Do this 3 times at 8 hourly intervals and its done.

Last step is to go over it with carnauba wax which is applied sparingly and immediately rubbed off leaving a soft lustrous shine. I use Liddy's available any where that wood finishing products are sold.

At this pont, after the wows are over, you need to carefully get stuck into fitting off the hardware and installing the chassis, speaker and rear panels. Hopefully with no added mojo or relic type scratches and dings to the finish.

The sequence of assembling goes roughly thus:
I like to fit a bracket to steady the chassis against the rear panel. This is optional. The next step is to fit the rubber feet and corners which will afford a deal of protection to the cabinet as it gets gets moved about and turned every which way a lot while the fit out proceeds.
Fit the chassis and mark the bracket mounting holes in the rear panel. Very simple while the speaker baffle is out
Tap in the teenuts for the handle and screw in the speaker baffle
Mount the speaker ensuring the terminals are in the best position for the speaker lead to avoid hot valves or speaker magnets.

Power plant in place. I've made up a speaker lead, and tested it with a multimeter. Powering an amp without a speaker load can blow the output trannie. The cables are tied off and all that's left is to install the valves and screw down the top panel.

Time to plug in a guitar and blow out the sanding dust. :) Definitely the funnest part of any build is that first 5 minutes of letting her rip


Above:You can see how I have secured the speaker and power lead so they are not flapping around loose inside the cabinet.

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