As the B4 VST has been discontinued (Except for Wersi OAS7 instruments) I find the best clone for a computer is the VB3 http://www.genuinesoundware.com/?a=showproduct&b=24 although with the editing available with Vintage Organs, (It has many advantages as it is a Kontakt Instrument) you can get it to sound as close as you want.

Bill
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English Riviera:
Live entertainment, Real Ale, Great Scenery, Great Beaches, why would anyone want to live anywhere else (I�m definitely staying put).