Amp Build
I built a tube amplifier. It is a small "studio" type amp of approximately 4W. I based it off an associated project at the AX84 web site called the October (click here), but modified it heavily for my interests. The following is a link to my schematics with power readings in red.
Please note that the website AX84 has transitioned to a discussion forum called "Guitar Amp Builders Forum". Currently as of the posting the old project information is now available at AX84 Archive.
I have powered it up. First time there was a high pitched squeal from the speaker. I went in and reversed the primary leads on the OT and squeal is now gone. However...
With the volumes maxed, the sound of the guitar comes in faint and heavily overdriven.
Someone pointed out the MV was the wrong value. I pulled the ground off the MV and left it at full and the volume came up a ways. Still low and distorted. Have some voltages I need to check and it was recommended to go back and look at the preamp and PI grid reference resistors.
I temporarily pulled the ground of the MV and eventually found a 1MA pot to replace it. I also found I had placed a resistor for the second gain stage cathode ground that was 100k and it was supposed to be 470. I replaced it and...
Wow. With the bright and dark volumes set to 1/4, the volume is as loud as you would want inside a house. Moving one of them up to 1/2 and you start to get nice creamy overdrive.
Nice and bluesy.
I built a head enclosure and a speaker cabinet. It is a 1x12 enclosure with an Eminence 12" Cannabis Rex 50W, open backed.
One of the things with this design is that both the preamp and the power amp sections are driven by triode tubes. This means that the over drive sounds are only what are traditionally thought of as preamp distortion.
I am considering reworking this so that the dark channel is a slightly brighter, and the bright channel is revised to be a pentode preamp tube. This would allow me to create a mix of triode/pentode distortion.
Images below.
Boards with turrets installed
Staking tool to install turrets
Boards soldered up
Boards soldered up
Chassis holes cut. Friend has water jet cutter for top openings.
Chassis back
Interior of chassis
Components installed in chassis - top view
Components installed in chassis
Starting wiring inside chassis
And more wiring
Starting to look like a rats nest
Wiring continues
Close up of wiring completed - Bias trim pot and power tube sockets
Close up of wiring completed - speaker jacks and ohm selector
Close up of wiring completed
Build Complete - Tested - Functional: Modifications? Experimentations? Who knows!
The amp enclosure and speaker cabinet mostly completed. I did add a grill to the back of the amp to prevent people from touching hot tubes. The faceplates were created by laser etching 1/8" thick maple plywood and then mixing ebony wood dust with wood glue, pressing into the etching and then sanding smooth. Guitar in background of left photo is the guitar I built. You can see the construction in the associated pages.
