I recently purchased as NOS a Bachmann HO EMD FT-A Southern Railway engine (11712).  Did Bachmann ever offer an FT-B unit for Southern Railway?  I am assuming the item number would 11812 by following the others FT-B's.
I would save me a lot of searching if knew for sure. 

I recently purchased as NOS a Bachmann HO EMD FT-A Southern Railway engine (11712).  Did Bachmann ever offer an FT-B unit for Southern Railway?  I am assuming the item number would 11812 by following the others FT-B's.
I would save me a lot of searching if knew for sure.   

As I said, the Bachmann "Type B" directional turnout switches have a small CD (capacitive discharge) unit inside them (2, 47µfd caps) which help with the switch operation.  With just the CD circuitry, without the pulse circuitry, you still need to use momentary switches to prevent continued triggering after the caps recharge (again depending on the circuits).

Buzzing turnouts are caused many times by not enough AC power coming from the accessory terminals when there is too many things connected to it.  This is usually corrected by using a CD power supply and push button or (on)-off-(on) toggle switches.

BUT, the regular turnouts (44561 & 44562) have the "Type A" control while all the rest have a "Type B." 

The A is basically a spdt slide with a monetary push-button and therefore will buzz and not throw if there is not enough AC AND one needs to be careful as to how long the button is held so as to not burn out the solenoid. 

The B looks to be a small CD circuit with additional circuitry to provide a proper, higher voltage, DC pulse with a dpdt slide switch without concern for the length of time the switch is held in position.

Why there are not the "Type B" switches in all, I don't know.

Check out:

http://www.youtube.com/watch?v=iR_-HkfJRik