CTH Wiring


The CTH has all off-board components except for the power inlet jack at the back of the board. The wiring is not complicated, but once again careful attention to the pad and wiring will be a good idea.

These wiring diagrams (courtesy of Ric Lee) show how to wire the various pads to the jacks, pot, and switches.

Board Wiring Diagram

CTH Wiring Diagram (JPG) CTH Wiring Diagram (PDF)

Here are additional diagrams with higher resolution that show the locations of the various pads with a text description below.

Board Pad Locations

CTH Wiring Pads (300dpi PNG) CTH Wiring Pads (600dpi PNG)

On the pad location diagrams the pad colors are:

  • Power Switch Pads - Blue
  • Heater Switch Pads - Orange
  • Input Pads - Red
  • Output Pads - Green
  • Star Ground Pad - Cyan
  • LEDs - Green and Red

Power Switch

  • The power switch is connected to pads S1 and S2
  • You don't absolutely need the power switch but you should use a fuse to protect the wallwart. If you use a fuse connect it to S1 and S2 and then turn the amp on/off by inserting/removing the plug

Heater Switch

  • The heater switch is a SPST type. It connects to H1 and H2
  • When the switch is open the heater supply will make 12.6V and when the switch is closed it will make 6.3V

Input Connections

  • The input connections are ILIR, and IG
  • Connect the left wiper of the volume pot to IL
  • Connect the right wiper of the volume pot to IR
  • Connect the ground wires of the volume pot to IG
  • The input jack(s) should be insulated from case ground

Output Connections

  • The output connections are OLOR, and OG
  • Connect the left output jack connector to OL
  • Connect the right output jack connector to OR
  • Connect the ground output jack connector to OG
  • DO NOT ground the jack. it MUST be insulated from board and case ground. The OG sits at 12V and connecting to ground will damage components

Star Ground

  • Star ground is the SG pad
  • Connect the SG pad to the case using a wire


  • The 3mm LEDs are near the relay. There are pads for two LEDs
  • One LED lights red when the ε12 is off and the other LED lights green when it is on
  • You can, obviously, wire panel mounted LEDs from these to sets of pads
  • You can also use a dual 3mm LED by wiring to the two + terminals of the LED pad and one of the - terminals
  • There is a hole under the tube socket for inserting a 3mm dual LED to light the tube.