Here’s the Holly Grail Maestro Boomerang from Joe Gagan personal collection. Thanks Joe for your contribution!
Here’s what Joe says about his unit:
“after careful examination of this unit and another that sold on ebay in feb ’10 ( they had serial numbers only 2 digits apart!), i am convinced that the unit pictured here is 100% original, all solder joints untouched. original pot. unknown inductor mfgr.
gibson seems to have rushed this into production in the same year as the famous vox. disreali gears and hendrix created a huge demand for these suckers. it uses a patent first applied for in 63 by richard petersen, a resonant circuit designed to imitate a voice or trumpet ‘wow-wow sound” ( gibson owned lowry organs had this feature by around 64). even the schematic uses the term wow wow instead of wahwah.it seems that very few actual BG1s were made, however, and the BG2 boomerang came out in 68.
the BG2 used a different inductor, different pot manufacturer, and doubled as a volume pedal when the wah was off. one of the worst tonesucking pedals in history. but for the wah sound- in my direct comparisons the BG2s still do sound very close to the BG1 voicing and response curve.”