British Pedal Company Tone Bender MK 1.5 VS

They say:

Often known as the mythical fuzz due to the very few original examples which exist, the MKI.5 Tone Bender was produced in 1966 and was the first tone bender that featured the iconic Grey Hammerite Aluminium Casing. The MKI.5 featured a different circuit than the earlier production MK I and consisted of a 2x OC75 transistor circuit At the time of production one of these rare fuzzes managed to find its way into Abbey Road Studios and was pictured being used by George Harrison of The Beatles.