Back in 2003, I found ax84.com, an opensource community for designing and building tube guitar amps. My goal was to build low wattage single-ended amp with wide tone/gain options and reverb. ax84 had a couple of schematics for low wattage single ended amps but none with reverb or tone variability beyond a typical bass/mid/treble tone stack. I settled on the Hi-Octane (http://ax84.com/hioctane.html) design for the basis of my design. It is based on the EL84 pentode power tube with 2 12AX7 preamp tubes and a tube rectifier power supply (4 tubes total). I wanted to have the ability to switch between two "channels" (rhythm/lead, clean/dirty, etc.). I decided I could achieve that by adding a switch between the first and second gain stages to allow bypassing the second stage and a pot to control it's gain. I then found a circuit for a Fender reverb driver/recovery and inserted that with some impedance matching between the tone stack and the power tube. That added two extra tubes (a 12AT7 and 12AX7 and a audio transformer). I added an adjustable bias circuit and my final mod was to add a switch on the EL84 screen to allow selection between pentode mode and triode mode for a more vintage/gritty sound. Many of the parts I used we're old parts from my late fathers part stash, including 4 switches, the jacks, the lamp/jewel and the brown turret boards.
Here's the some amp porn:
Here's a closeup of the tone stack, and reverb driver/recovery circuit:
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