IainStinson wrote:B&F did some "interesting" work with pneumatic action instruments. Before Nicholsons rebuilt the St Anne organ it had B&F "Transformers"; these were rather like "blind" general pistons which were usually placed about the top manual and could be drawn to provide registrations across the organ - they were engaged with a a dedicated stop which cancelled the current drawn registration and use the selection made by the transformer stops.
I sometimes play a 3m B&F in my town church. The console was on display in Chappells Music back in the early 1900s as an example of how advanced the B&F consoles were. It's, as Iain describes, "interesting" to play. There are what look like conventional pistons in the keyslips, but they actually turn out to be pre-defined "blind" pistons. e.g. pushing one of them will give you Great OD1 + Principal, and completely disregard any other stops you have pulled out. This can make for quite creative registering - whilst you've got the blind piston engaged, you can change anything you like by hand, and nothing will happen. Disengage, and your hand registration comes back.
The only indication that you've got one of these blind pistons pressed is a little flag board next to the great stops that go white or black depending on what you've got pressed.
Above the top manual there is a row of ventils that also give whole organ combinations, e.g. "Flute Celeste", "Orchestra", these are on draw stops, and there's a separate stop that you draw to engage those ventils. They call them Transformers, and here's the list of them: Viole Celeste, Flute Celeste, Principal Celeste, Woodwind, Orchestral Chorus, Reeds, Flues, Grand Chorus, Flute Solo, Oboe Solo, Clarinet Solo, Horn Solo,
Free Pedal, Free Accompaniment.
All rather complicated, but rather good when you get the hang of it.
Picture below:
http://www.npor.org.uk/cgi-bin/PSearch.cgi?Fn=PSearch&rec_index=N11407&no=1