Dave’s Homebrew
I decided to build a guitar amplifier from the ground up so I could learn about them. I chose a design based on a Fender Princeton that uses a common 6V6 vacuum tube in a Class A configuration. I had been researching the possibility of buying a kit amplifier and found the AX84 Project. There were kits available for their P1 design and I thought this was a good place to start because of the difficulty in locating all the required parts. I soon found out about a local business, Antique Electronic Supply, that could provide one stop shopping for my tube amp needs. I went one step further and decided to make a slightly different version of the amplifier design I found on the internet. I wanted more tone control than was available on the Princeton clone design so I found the Champ schematic had most of what I desired. I would be combining some of the AX84 P1 preamp design with the Princeton/Champ output section. I also decided to experiment with the feedback from output to preamp as in the Fender amps and try adding a ‘Master’ volume control.
I was extra careful in the grounding and power distribution scheme which led to a surprisingly quiet amplifier. I based it on the Champ, but added an additional input with attenuated gain, a midrange control, a master volume, and a standby switch. I used a solid state rectifier and ended up with about 390 volts on the plate of the output tube. This led to the decision to use a 6L6 power tube instead of the 6V6 as in the Champ.
The decision to implement a master volume was not as expected. I wanted to be able to play the amplifier and get distortion at low volumes by overdriving the input stage tube. Unfortunately, there is not enough gain between the two stages to get into the overdriven mode. I use my Ibanez TS-9 Tube Screamer to overcome this, but I wasted a potentiometer in the process. I may tweak the gain on the two input stages as an experiment one day.
Click here for a hand drawn schematic