My wife Nyree has been wanting to play the guitar for a while, but has been frustrated teaching herself. I found someone to give her lessons, but needed something more tangible to give her for a birtday present. What a perfect excuse to build a neato tube amp!

I found this design on the Angela Instruments "How To" section a while ago, and have been wanting to build it. Guitar amps are such cool pieces of equipment since they are essentially self sufficient stereo systems. Better yet, they are often designed to be un-linear and to intentionally distort. A perfect project!

This is basically a redesign of a 1950s Fender Princeton, modified slightly by Angela Instruments to use available parts. It is a single 6V6GT driven by a 12AX7. Original Princetons have the controls mounted on the top rear of the cabinet, but I wanted a little more room to work inside the chassis so I built the cabinet in a more common front mounted controls configuration.

I used Fender Tweed and grillcloth to upholster it and used a leather handle for that retro look. I am still searching for the perfect knobs though - maybe some brown chickenheads or something pearl-ized. The cabinet is 3/4 plywood with 3/8 plywood speakerboard and rear panels. I used weldwood contact adhesive to glue on the tweed and it basically sucked, so if anyone has a better way to attach tweed, please let me know - there should be a mailto around here somewhere :)

The circuit uses parts almost exclusively from Angela Instruments. I was working under a deadline, as this was a present, so I tried to get everything in one order from Angela. Unfortunately I didn't write any quantities on my parts list so I was short a few resistors and capacitors, which I had to get from Radio Shack. The pilot light and switches are also from Radio shack. The small switch in the center of the control panel is a feedback in/out switch that switches the feedback loop in and out of the circuit. I was surprized to see feedback on an otherwise simple and elegant circuit so I tried building it with a switch first to see what it sounded like without feedback. The sound was noisier and livelier and it seemed that the distortion came on a bit earlier. In short looser and more raw. I liked being able to switch between these sounds, so I drilled another hole and mounted the switch.

Check out that neato old school Fender reissue speaker with Alnico magnet!

This was the first project I have built from a schematic and pictorial only, and so I made a few mistakes at first. After I fixed a problem with the filament wiring, I hit the power switch to smoke check it and after a bout 20 seconds of warmup, it began to make a high pitched warbling buzzing sound! I nearly peed myself and shut it off immediately. Did I mention that there was no speaker hooked up? The sound was coming from the 6V6! Being the fool that I am, I tried powering it on again, just to see if the problem was "reproducible" (hoping it would magically go away). Same sound, and boy is it nerve wracking to have a tube make a sound like that. At this point some troubleshooting was in order. Maybe I had screwed up my handy dandy feedback switch - I switched the feedback circuit out of the loop and fired the amp up again.... Wait a second... No sound yet... Hey, no scary sounds - it must be the feedback loop. I switched the polarity of the speaker output so that the feedback return lead was on the other lead of the OPT and now it works like a champ (pun intended - the Champ is a Fender amp of the same vintage as the Princeton). Amazingly, the 6V6 still works. There is a bit of bubbling and hiss, so I think I will swap it with a 6V6 that has never made a scary sound. Luckily, Angela included a variety of tubes above what I ordered and paid for so I has replacemants on hand. I would recommend Angela Instruments to anybody. Those folks are the best.