Please assemble a cable according to the drawing below. The components are available from most electronic parts suppliers. Please note that this interface is different from the one for the Pro Tube Twin Amp. A skilled technician will be able to fit the components inside the housing of the jack connectors (We can recommend Neutrik NP2C(mono) and NP3C(stereo) jack connectors as they offer space for the components and superior strain relief).
Relay 1 open and Relay 2 open = distorted ONRelay 1 open and Relay 2 closed = crunch ON Relay 1 closed and Relay 2 closed = clean soundRelay 1 closed and Relay 2 open = clean soundWith thanks to Mr. Yves Martini