Chassis Selection

Without doubt, there will be several aspects of this project that are going to be trial-and-error. That is the nature of DIY projects. However, I am trying to minimize the money-wasting aspects. One way I have found that helps is to build the project in your mind and on paper several times before you ever purchase or cut the first piece of material. 

This tactic is going to be invaluable during the creation of this amp, especially regarding the chassis design and cabinet construction. 

My previous sketches called for a chassis made from a 12"x8"x2" steel project box. I have since located a supplier for many more sizes and materials. My latest sketches include an aluminum box (also made by Hammond Manufacturing, the same company that makes the other steel boxes) that measures 17"x4"x3". After some sketching and figuring, this shape is much more conducive to this particular project. Also, aluminum doesn't rust, and comes uncoated/unpainted, which would prevent me from having to sand off the paint from the steel box at all points where an electrical ground would be attached. 

After doing some web-based research, I've discovered there is quite a debate over using aluminum vs. steel boxes for amp chassis. I sifted through post after post and finally concluded that either one should be sufficient, as long as I brace the section where the heavy power transformer and output transformers are to be attached with a stronger, thicker metal of some kind (which I'd already planned to do). The good news is that this new aluminum choice is roughly the same price, maybe a little cheaper than the steel counterpart. 

I'm working on drawing up some plans for the entire contraption, cabinet and all. I will post those pics as they are done. 

Preliminary Cabinet Design

I realize that I'm going to need to figure out what kind of cabinet I want to put this amp in before I can begin to assemble the chassis. Because of the style of project box I chose, it looks like it's going to be smartest to make a vertically-mounted chassis (like the old tweed Fender amps). I'm doing it this way for two reasons: because it's going to work best with the parts I've chosen, and because this way I'll have the opportunity to design and build my own style amp rather than completely copying the Vibro Champ. Pride in originality. Below is a sketch of what it might look like, from the rear:

As you can see, the chassis will sit vertically with the tubes protruding towards the floor. 

Another cost-saving feature of this arrangement will be the cover of the project box. Since it can be covered by the back (wooden) panel of the amp cabinet, I don't need to purchase the costly sheet metal cover to match the project box. 

At this point, I am fairly certain I'm going with a 2x8" speaker configuration. However, that can be decided for sure much later, after the amp chassis is assembled. As long as I'm pretty sure I want to make the chassis sit vertically like this, I don't have to make final decisions on speakers and exact cabinet size until later.

Parts List, Pt. 1

I've finally gotten around to finding most of the parts I need to get started. This list is not complete; I haven't included any of the resistors/capacitors or tubes yet. Basically this list gets the chassis rolling (so to speak), and it doesn't include any parts for the cabinet, either. 

Partial Parts List, Part One:

Power Transformer*          $35.00

Output Transformer*       $20.00

Circuit Board#                  $34.95

Power Switch                     $3.75

Pilot Light Assembly          $6.00

Potentiometers:

1. Intensity 25K Rev.Audio* $1.80

2. Speed 3.0M Rev.Audio*   $1.80

3. Bass 250K Audio*           $1.80

4. Treble 250K Audio*        $1.80

5. Volume 1M Audio*         $1.80

Input Jack (1/4" Mono)§       $.95

Tube Sockets:

1. Octal (2 qty.)                 $5.00 ea.

2. 9-Pin (2 qty.)                $2.50 ea.

Fuse Assembly 1A Slo-Blo   $2.50

Fuse 1 Amp Slo-Blo             $.60

Project Box (Chassis):

12"x2"x8" §                       $25.68

Wire: (6 ft. ea. color)

1. Green 18 ga.                   $.50/ft.

2. Black 18 ga.                    $.50/ft.

3. White 18 ga.                    $.50/ft.

4. Blue 22 ga.                      $.50/ft.

5. Red 22 ga.                       $.50/ft.

6. Yellow 22 ga.                  $.50/ft.

IEC Power Connector             $1.50

Total: (ex. tax and shipping)  $174.73

All parts from AmpWares, except:

* Weber Speakers

# Triode Electronics

§ Parts Express

If you need part numbers or more specifics, contact me.