Valve Commander Low Voltage Tube Guitar Pedal DIY

Welcome to my low-voltage "Valve Commander" tube pedal build.

After building the low voltage (12vdc) Valvlitzer and Valvecaster 2.0, I set out on this journey to improve on both designs, and I call it the "Valve Commander". This is a 100% analog dual-tube, low-voltage guitar pedal. No transistors, IC's or digital parts are required! The Valvelitzer and Valvecaster have a very classic tube sound, but overall I wasn't too impressed with the overdrive tone. I prefer more overdrive and sustain than they had to offer for lead guitar tones.

The Valve Commander uses two tubes in series to increase the gain. It has a great lead sustain and a fat tube tone. If you add delay and reverb, it has a silky violin sounding sustain, similar to that iconic Eric Johnson tone. I run mine through a solid-state Fender Mustang which has built-in effects. I included a video of the pedal and its different tones.

I used 12Fq8 Dual Triode tubes like the Valvelitzer. They are cheap ($5-$10 on eBay) The two tubes are assembled exactly alike which keeps things simple. I used a 12VDC wall wart that I had lying around. I also added a 100K pot between the two tubes. This pot allows you to adjust the overall overdrive of the pedal. Turn the knob down and you'll get very mild dirty tones from tube #1, turn it up and the overdrive through both tubes is surprisingly amazing. The last thing I did was add a bypass switch and an LED to let you know the pedal is on or off.

To increase clarity I used a smaller value 4.7nf (.0047uf) coupling capacitors throughout and reduced the cathode resistor/capacitor circuit. This simple change removed a lot of the muddy bass sounds I found with the Valvelitzer.

If you are just starting out I would suggest building the Valvecaster first since it is only one tube and a very basic circuit. You can always use that tube for this project when you are done!

So lets get to it! I hope you enjoy!

1. 12FQ8 Tubes & Sockets
2. Assortment of 1/4 W resistors / Assortment of coupling capacitors
3. 100K Pot
4. 12VDC power supply
5. 1/4" input / output jacks
6. Wire
7. LED Light
8. Bypass Switch
9. Soldering Iron / Solder
10. Project Box
11. Multimeter

The diagram above shows a closeup of one 12FQ8 tube section. The image is as if you are looking at the bottom of the tube socket. The 12FQ8 is a dual triode tube, so the signal path goes in one grid (Pin 2), and then out of the tube (Pin 1 & 3), through the .01 Capacitor and into the other grid (Pin 7), and then out of Pin 6 & 8. It's like two tubes in one. You will need to build two of these!

I suggest building the tube circuits individually like the above image and then connecting the two tube circuits together later on. It is completely up to you, but I find it is easier to keep track of where I am at when building one circuit at a time. Just like the Valvelitzer or Valvecaster, you can solder the resistors and caps directly to the tube socket to keep things clean. These small components can be tricky to position and solder, but I have confidence you can do it! I suggest using solid core wire because it is stiff and you can form it around the pedal box. 24ga solid core wire will work well.

Above is the full wiring diagram of the Valve Commander. After assembling both tube circuits, I suggest planning your layout within the project box. You can mount the sockets to the project box, or leave it loose to make wiring a little easier. One of the trickiest parts is how to run all wires cleanly without it looking like spaghetti. At this point, assemble and wire the on/off switch, the bypass switch and the 1/4" Jacks. Be sure not to miss the 1M Ohm resistor at the guitar input. You can see it attached at the input jack. Connect all grounds

1. Using a multimeter, double-check all connections and resistors to be sure they are all reading correctly.
2. Make sure all grounds are grounded to the same ground. All grounds must be grounded to each other.
3. Be sure no components are touching each other causing a short.
4. If you are sure everything is wired correctly, you can power up the pedal!

There are many ways to make this your own pedal. See the diagram above for changes you can make. I would suggest using a breadboard to test the sound before soldering it all together.

You can:

1. Change the 470K & 1M resistors load resistors. Increasing them will increase the distortion but it will also lower the output of your guitar signal. Eventually, the output will be quiet and very low volume.
2. Change the 10K cathode resistor from 5k to about 20k ohm and the cathode capacitor from 4.7nf up to 10UF. Since you have two tubes you can do a variation between the two.
3. You can change all coupling capacitors from 4.7nf (.oo47uf) to a .01uf. The bigger the capacitor, the more bass you will receive through the audio signal. Go too big and you'll end up with a muddy-sounding circuit.
4. You could also bypass the second tube, and the first tube acts like a booster pedal, boosting the signal, but not distorting it much. The possibilities are endless! Have fun and rock on!

1. Test each tube circuit before assembling it into the pedal box.
2. Be sure all grounds are connected to each other.
3. If your pedal is noisy, try switching to a different wall wart. Some are noisier than others. There are other ways to reduce power supply noise with filtering caps, but with the right power supply it should be quiet. I had two wall warts, one was super noisy and the other was very quiet.
4. Noise can also come from RF. If you are testing the tubes out in the open, make sure there are no electrical devices around, especially motors like compressors or fans. Once the tube is in the enclosure, a lot of that RF will be blocked.