In normal phase HPLC, the mobile phase is relatively non-polar and the. stationary phase is relatively polar. Other more general types of HPLC include partition, adsorption, ion-exchange, size-exclusion, and thin-layer chromatography.
This particular guitar loop pedal is the Boss RC-30. Simply put, a loop pedal is a device used to capture sound clips which are then played over and over again (looped) and often overdubbed. While loop machines have been around for quite a while, the idea of a guitar loop pedal is relatively recent. Instead of the traditional box controlled by the hands of a DJ, loop pedals allow guitarists to control the looping and overdub features via foot switches.
Preamp tubes are the smaller ones. Their function is to add gain or increase the guitar signal in the amp. Most common is the 12AX7, aka ECC83 and 7025. 12AT7 is also fairly common. Others are also used occasianally. Like the rectifier tubes, they have a very long life and rarely wear out. Sometimes they will stop working causing various symptoms.