Apr 3, 2026

Guitar Tube Amp and Speaker Cabinet

After a bunch of analog and digital pedals, it was time to tackle vacuum tubes and an amplifier!

I wanted a Marshall style JCM800 amplifier, but for home levels, I did not a full 50W of output. I found this 1W kit from Mojotone and it was exactly what I was looking for.

https://mojotone.com/products/mojotone-studio-one-1-watt-2-channel-guitar-tube-amp-kit

I did not allow myself to start building this until I understood every aspect of the schematic.

Resources used for learning: https://robrobinette.com/Amp_Stuff.htm https://www.youtube.com/@UncleDoug/videos

The changes I made to the schematic/wiring were:

  • Added a 1M pulldown resistor at the output of the clean channel before it goes into the relay to avoid footswitch pops when changing channels
  • FX loop
    • IN/OUT inserted between the relay out and the 22nF capacitor with shielded wires
    • Power supplied by XB at the filter capacitor with an inline 4.7k resistor
  • Ground the input to the dirty channel when the clean channel is active to prevent any crosstalk/distortion in the background
    • Separate shielded wire, with a 68k grid stop resistor, from input jack to input of grid (V1A) for clean channel
    • Separate shielded wire from input jack to unused common of 2nd pole on the relay switch board
    • Shielded wire from 2nd pole on the relay switch board when dirty channel is active, to the input of grid (V2A) with an inline 68k grid stop resistor
    • Ground wire from 2nd pole on the relay switch board to ground (on master volume pot) when clean channel is active

Transformer specifications:

Time to start assembly of the turret board. First I used an oscilloscope and my fingers to identify which lead was for the outer foil for each capacitor.

https://www.nutsvolts.com/magazine/article/finding-the-outside-foil-lead

My oscilloscope wasn’t quite sensitive enough, so I actually amplified the signal a bit with a J113 JFET and that worked perfectly, very easy to determine which lead was the outer foil when I pinched the body of the capacitor with my fingers.

Even though they are non-polarized capacitors, you can orient them in a specific way to reduce noise even further.

Turret board completed.

Wiring the heater circuit for the tubes and the power transformer.

Start to populate more of the components and wire them up for the input side and the output side.

I added a FX loop so that I can use modulation effects with the overdrive/dirty channel of the amp.

Filter capacitor all wired up.

Time to build a cabinet for the head.

Clearance is clearance?

Time to make a speaker cabinet next, I wanted a single 12" Celestion V30 speaker, with a closed back cabinet, and an option to open the back.

Overall this was a very fulfilling project, I learned a lot and it sounds great!