Mesa 5U4 | 5U3C | 5U4GB | 5C3S | 5AS4A. This is the earlier Mesa version ST shaped tube used in older Mesa Rectifier amplifiers. These are unlabeled but came directly from the Mesa factory. Getting harder to find so stock up now before they are HISTORY.
One of the finest rectifier tubes anywhere. No longer made and soon will be gone forever.
Tested on the RoeTest professional computer testing system.
CALIFORNIA PROPOSITION 65 WARNING
WARNING: Cancer and Reproductive Harm-www.P65Warnings.ca.gov.