Complex sentence: It is very similar to the octal base EF37A and the Rimlock base EF40, and was used in many preamplifier designs during the last decades of vacuum tube hi-fi development.
Split into simpler sentences: It is very similar to the octal base EF37A and the Rimlock base EF40. The EF86 was used in many preamplifier designs during the last decades of vacuum tube hi-fi development.