From PL website:
PrimaLuna uses ceramic tube sockets secured to ventilated steel plates that are bolted to the chassis. The entire signal path, including resistors and capacitors, is painstakingly hand-wired with heavy gauge cable by craftspeople. In our EVO 300 and 400 models, we even use Swiss-made silver-plated oxygen-free copper cable with a Teflon dielectric in the entire signal path. The result is a product that sounds amazing and lasts for decades.