BTR2 recorder (1954–1970)

The BTR2 is a mono tape recorder, created as replacement for the
older BTR1 machines. It was quite a success, with hundreds of
units being built and used worldwide by EMI studios and the BBC.
It was the workhorse machine for most Abbey Road recordings
from the 1950s and '60s.

The studio engineers devised clever ways of creating audio effects
by manipulating the BTR 2 recorder functions. This created echo,
doubling, and 'flanging' effects. The BTR2 machine was responsible
for many of the psychedelic effects of the late 1960s.

"Courtesy of EMI Group Archive Trust a charitable organisation which
preserves the early heritage of The Gramophone Company and EMI"