The Berkeley signal path is almost exactly identical to the original late 60’s vibe. Carbon film resistors, Mylar caps, transistors chosen for very very similar or identical characteristics to the originals. Some small key changes have been made in line with mods that were done in the late 60’s to open up the low-end and add more liquid movement. There are 4 photocells, but no bulb. Hand chosen Vactrols are matched one by one in a custom test fixture to make sure that every component works within a well defined ‘sweet spot’ range. No guessing here.