Searching through a used amps website I found this Bouyer ST10 PA amp at a great price. These were made in France during ’62 to ’71. They are equipped with an EF86 and a 12AX7 in the preamp section, single 6L6GC in the power amp and an EZ81 rectifier. Sure enough, they make great candidates for a powerful single ended guitar amp project. I modified and used the amp in it’s original bulky chassis but after a while I decided to rebuild it into a compact head amp.
If you have no metal working skills like me, making an amp chassis from scratch is next to impossible. But I remembered seeing some people building amp circuits into cake pans. The so called “cake pan amps”. Cruising through specialised cooking store websites 🙂 I found a dead cheap aluminum bake pan just perfectly sized to become a house for tubes, transformers and the like. Even the metal panels of the Bouyer fitted just right on the pan’s sides.
After some measuring I fitted the transformers and drilled the holes for the potentiometers, switches etc.
The circuit is quite simple but still versatile: for the first gain stage you can switch between a clean 12AX7( one half) or a higher gain EF86 pentode. Then the signal goes to the other 12AX7 half and finally to the 6L6 which is cathode biased at around 15 watts. I also added a switch that lets you add the cathode bypass capacitor for a louder-fatter sound or remove it for more controllable volume. The three pots are for preamp gain, tone and master volume. Finally, I changed the rectification to solid state to up the voltages and not have to worry about replacing a rectifier tube along the way.
The third 9-pin tube socket is for a tube I had salvaged from an old radio and was itching to use. It has no practical use but is a nice little gimmick. It is an EM84 magic eye tube which lights up according to the signal level! It was used in old radios etc as a VU meter.
The wooden amp head was built out of some scrap plywood and painted(quite poorly) with thinned acrylic paints. I paired the amp with an Alnico P12N speaker in a compact cabinet built the same way. The whole thing sounds great and has quite some power for it’s single ended nature. Here’s a small demo below, with the magic eye tube in action!
This Post Has 7 Comments
Hello there, I really like what you do with breathing new life in old bits of gear, do you take in any projects?, I have and old filmosound that I want converted into an amp, I don’t know where you are based,are you in th UK?. Thanks Keiran.
Hi Keiran, I’m based in Athens, Greece.
Send me an email at firstname.lastname@example.org and we can discuss this further.
Hello there, I really like what you do with breathing new life in old bits of gear, do you take in any projects?, I have and old filmosound that I want converted into an amp, I don’t know where you are based,are you in th UK?. Thanks Keiran. P.s the proper e mail has the number 45 in it not 43, sorry I made a mistake.
I just bought a Bouyer st10 amp.
I would like to build a guitar amp
Do you have a circuit diagram of your amp?
Hey, I sent you an email. Thanks for your comment.
What a great job! And what a great sound! I’m having the chance to get a st30 and convert it into a guitar amp. But i can’t find anywhere what kind of mods are needed. Would you help me with a brief explenation or with some schematics?
Hi Rui thanks! I appreciate it.
I would gladly offer any advice I can but first I have to ask how experienced you are on working with tube amps! The high voltages in it are no joke and also the amp could be damaged by wrong wiring, shorts etc.
Having said that there is a chance that the amp sounds good as is if it’s working properly. In any case send me an email if you like and we can discuss this further. Thanks for your comment!