EMI HB-1E microphone (1930s)

The original model of this microphone was named HB-1A,
designed by EMI engineers Herbert Holman and Alan
Blumlein. Later B, C and D versions were built as well.
In most photos of Abbey Road in the 1930s and '40s,
these HB models are the microphones being used.
Sometime later EMI's Reg Willard created a final version,
the 1E - only one was ever built, and it survives and 
functions to this day.

(quotes from description)

Microphones

Since the 1930s, microphones have been a key element in any 
recording session. They are the 'ears' of the studio, as they
transform sound into electronic signals which can then be recorded.
Abbey Road Studios' large collection of microphone is one of the
best in the world.

Vintage microphones are extremely valuable and prized by any
studio. Abbey Road's unique collection comprises a large number
of originals, spanning decades. It is a working collection, as the
microphones used on recording sessions today are often the very 
ones that have been used by legendary artists throughout the 
studios' long history.