Intro: Amp in Case Reproduction Guitar Case
The Project - An Old Guitar and Amp Need a New Home
In the 1960's Sears sold a Silvertone-made guitar complete with a hard shell case with a built-in tube amplifier. A blues-guitar playing friend of mine acquired one a few years ago, and though the guitar and amp worked well enough, the case was falling apart and unusable. I offered to fit the amp in a new case and after failing to find a suitable off-the shelf case, I decided to make my own so that I could custom fit it to the guitar, amp, and speaker. The finished case is about 50" by 14" by 4". I didn't have the guitar on hand to build the case and fit the interior, so I relied on a tracing that I did when my friend was visiting, and occasionally called him to measure specific dimensions on the guitar. This was especially necessary when finishing the inside of the case and fitting the guitar support blocks.
I built the case from baltic birch plywood and covered it with black Tolex (fabric reinforced vinyl) and lined the interior with red velvet. I also made my case a little deeper than the original so I could fit an Alnico magnet speaker in place of the original, less efficient ceramic magnet speaker. The replacement speaker is a vintage Jensen that I salvaged from the curb when a local business threw out all of their old Muzak speakers. With the extra case depth I also made a false bottom for storing cables and such, and included a small Tolex-covered and velvet-lined compartment for my friend's harmonica mic and footswitch.
Planning the Case
Since I still had the old case, I simply measured the inside dimensions as the starting point for the new one. I planned to use a speaker that was deeper by about 1 inch, so I added that to the depth of my case. However, because the case needs to fit the guitar snugly to prevent it from banging around while being carried, I decided to include a false bottom that would take up the extra depth and provide a space for storing cables, cd's, whiskey flasks--whatever a travelling blues musician needs.
Building a Plywood Box - the Easy Part
I made the box with 1/2" sides rabeted, glued, and stapled at the corners, and with a 1/4" top and bottom that was also rabeted, glued and stapled to the sides. I then split the box into a top and bottom on my tablesaw, and glued and stapled the amp mounting boards into place. I cut the speaker hole with a circle-cutting jig on my plunge router and rounded the speaker cutout with an 1/8" radius roundover bit. I used speaker mounting studs salvaged from the original case, inserting them into countersunk holes from the outside of the case. I filled all of the staple holes with 2-part wood filler, then finished the box by rounding the outside corners with a 1/4" roundover bit and sanding everything smooth.
Covering the Box with Tolex - the Basics
To cover the box, I chose to use Tolex and to glue it with water-based neoprene contact cement. If you're not familiar with using contact cement, it's an adhesive that you apply to both mating surfaces. You let it dry (enough so that no adhesive comes off when you touch it), then carefully align and join the pieces. You have to be careful with this step because once the mating surfaces touch, you cannot reposition them. You also have to make sure that there are absolutely no wet spots in the adhesive when you join the pieces, or the pieces will fail to bond completely and you will have bubbles in the Tolex. I learned this the hard way with the first piece of Tolex, but was able to correct the bubbles by working over the problem areas with an iron (I protected the Tolex with a piece of cloth). This was a tedious process, so I took care not to repeat that mistake with subsequent pieces.
Getting Good Corners - Patience and Planning Required
To simplify things, I glued the Tolex to the case in 2 stages--gluing the large top surfaces first, then dealing with the complexity of wrapping the covering over the sides and ends of the case and into the interior. In the interest of durability, I didn't want a seam right at the corner, so I joined the 2 pieces with a 45 degree cut on the end of the box, and this added a little complexity to the process of wrapping the Tolex around the sides of the case. After gluing the Tolex to the top surface, I then used a wooden template to pre-cut the corners to approximately fit (before applying the rest of the adhesive). I made the template by "wrapping" one corner with paper and cutting the corners the way that I wanted. I then made a sligtly oversize plywood template based on the paper test piece. After marking and cutting the corners using the template, I applied the adhesive to the remaining areas of Tolex and the outside and inside of the case sides. After allowing the contact cement to completely dry, I wrapped one side at a time, and trimmed the corners to a final fit as I wrapped the adjacent side. I ended up with pretty good fit overall, and I filled the few slight gaps from errant cuts with liquid electrical tape, which bonded very nicely to the Tolex.
Wrapping the Tolex for a Round Speaker Grill - Heat Gun to the Rescue
The other interesting challenge was the cutout for the speaker grill. I wanted a round hole and had no idea how I was going to finish it, but I ended up being able to heat the tolex and stetch it enough to be able to fully wrap the speaker hole. The pictures give a pretty good idea of how I cut the Tolex for this step. When the adhesive was ready, I heated the Tolex with a small heat gun set to low and slowly worked it around the case edge, gently stretching and wrapping the Tolex to the inside of the case. For the grill cloth I used a piece that I salvaged from the original case, and which I mounted directly to the speaker mounting board using contact cement. I was really happy with the nice clean look of the grill.
Prepariing a Snug Home for a Vintage Tube Amp - a Little Metal Work Required
Once all of the Tolex was glued, trimmed, and touched up where necessary, I prepared the inside of the case to receive the amp. I cut and bent a piece of aluminum flashing to go behind it (it also goes up the mounting blocks and over the tops of them, so the amp faceplate rests against the flashing when the amp is mounted). The flashing shields the amp from electrical interference (hum) and protects the case top from the heat produced by the tubes. I basically copied this configuration from the original case. I also glued a small piece of Tolex above the amp mounting area.
Finishing the Hidden Spaces and Installing the Hardware
For the case bottom I glued 3/4" x 3/4" poplar strips (painted black) along the inside perimeter of the case, and added another strip near the middle to support the false bottom and divide the bottom into 2 compartments. I used Liquid Nails construction adhesive for this. I then made the mic and footswitch box which I carefully fitted to the case to ensure that it would not interfere with the fit of the guitar. After marking the position of the box, I cut the velvet to fit the case bottom, then used 3M spray adhesive to glue the lining in place. I left the wood below the mic and footswitch box bare, and glued the box in place using Liquid Nails contruction adhesive. I fitted the case with new hinges, clasps, lid stays, and chrome feet (to protect the bottom of the case), and was able to reuse the handle from the original case.
Making the False Bottom and Top Pad - Foam Padding and Velvet to Keep that Old Silvertone Safe
With all of the hardware in place, I made the false bottom for the case from another piece of 1/4" birch plywood. After cutting it to fit around the mic and footswitch box and the lid supports, I used my router and circle cutting jig to cut a hole for the back of the speaker, and spray painted the back of the board black because I didn't plan to cover it with velvet. I then padded the top of the false bottom with some 3/16 craft foam (which is available in 24" wide rolls), and covered the foam with velvet, which I wrapped around the edge of the plywood. Using measurements taken from the guitar, I cut one walnut block to support the neck and hold the guitar in place within the case, and another to hold the guitar body away from the right hand lid support. I finished them with spray lacquer, and covered the support surfaces with velvet. I screwed them in place on the false bottom. The last bit of interior work was a velvet-covered pad for the lid. This was required to hold the guitar gently in place, and I made it by gluing some urethane foam to a piece of the craft foam. I then shaped the edges of the pad to form a nice, beveled pillow-like shape, and then covered the pad with velvet using the spray adhesive. I glued the pad to the inside of the case top using contact cement.
Installing the Amp - A Few Upgrades Along the Way
Before installing the amp, I replaced the original cord with a removable, grounded cord that I salvaged from a defunct computer power supply, and replaced the knobs that were missing from the original. To fit the removable computer cord I had to cut a rectangular hole in the face of the amp, which I did by drilling holes at all four corners and then cutting the sides of the rectangle with a metal-cutting jigsaw blade.
Looking Back at the Project - Money, Time, Tools and Results
My friend and I ended up spending about $100 on the project, for the plywood, contact cement, Tolex, velvet, spray adhesive, foam and hardware. I completed it over the course of 3 or so months, working when I could on the weekends and a few weeknights. To build the box I used my tablesaw, router, air-powered staple gun, orbital sander, and a few clamps. For the Tolex and interior I used a razor knife, straight edge and bread knife (to shape the foam pad), as well as a couple of foam brushes to apply the contact cement.
I was very pleased with the results, and my friend was pretty much overjoyed. If this Photo Instructable inspires you I'd be happy to answer questions and provide more details on how to fit the case and how I did the corners (though I'd need to have my friend take some closeups of the glued corners). Of course to start you'd either have to build your own compact tube amp (which I might do down the road), or pick one of these up on eBay or from a local Goodwill. They show up on eBay occasionally--search for "Amp in case" or "Silvertone 1457". There's also a model 1448, but the amp in that one lacks a transformer, and I wouldn't recommend using it since transformerless tube amps are kind of hazardous.