Here are pictures of the guitar amp I built using plans from The Cooperative Tube Guitar Amp Project web-site. The circuit design is the result of several people's input. It is the first of probably several amps that will be designed by the participants of the project. I urge you to visit the site as it contains a wealth of information and is frequented by some very friendly and knowledgable people.
The cabinet is made from pine and finished with a rust orange stain followed by a couple coats of clear satin polyurethane. This is by no means an ideal cabinet as it is very easy to dent. However, it will mostly sit around the house so it should hold up ok. Maybe next time I'll try to tackle a Tolex covering job. The grill cloth is Fender beige/brown/gold and the handle is a brown leather tweed era type. The knobs are cream colored chicken head pointers.
I've drawn up some plans for the cabinet which are available in a front and a back view. You should be able to get the top, bottom, and sides out of a single 1"x10"x6' board (which is really 3/4"x9 1/4"x6'). The speaker baffle is 3/4" birch ply, and the other wood is 3/4" square firring strip. The wood protecting the back side of the amp is 1/4" thick. The front and corner edges were rounded with a router, the back was left flat.
The chassis was purchased from one of the AX84 Project participants. It's made of aluminum and has cutouts suitable for a number of different layouts and configurations. It is held in place by 4 "L" type brackets, which you can just make out in the photo below. The cabinet holds an Eminence 12ALK speaker. It has an Alnico magnet with 1" voice coil and Kapton voice coil former for 35 watts of power handling. The speaker baffle is 3/4" birch ply. I had already cut out a baffle from 1/4" ply but then read somewhere that this isn't thick enough and that 3/4" is more appropriate. The speaker is mounted to the rear of the baffle and I rounded the front side of the hole to give a sort of "flair" to the opening.
The amplifier uses two vacuum tubes. The preamp is a 12AX7A which handles the first two gain stages. The power tube is an old National brand EL84 I had, which provides around 5 watts of power. The output transformer is again from one of the AX84 Project participants. They were special built to provide more bottom end than the available Fender Champ replacement transformers that propably would have been used otherwise. The amp has a switch on the back to select either pentode or triode mode operation. The amp has more power in pentode mode but has a slightly different character in triode mode.
Here's a picture of the amp next to a guitar I built. Actually I built the body. The neck was purchased already fretted. I had wanted to build a guitar amp for some time. In college I built a small transistor amp, but it wasn't very useful for electric guitar. The AX84 sounds great. It breaks up nicely as the volume is increased and has quite a bit of distortion at full volume. It turns out that 5 watts is quite loud. I had been looking around the Internet for guitar amp kits when I came across the AX84 Project page. It's a good project for someone with at least a little bit of soldering and electronics experience. The schematics are on line and there's a question/answer forum to get you through any tough spots.
Feel free to e-mail me with any questions or comments.
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