Placement of 6 amp 800 watt bridge rectifier

Why would you need such a large bridge?  A 3A bridge should be more than sufficient!  Cut at the red X in the diagram below and put the bridge in series with that wire.  For the bridge, you wire the + and - terminals together and wire the two ~ terminals in series with the wire.

Thank you very much.  This really helps me.  I chose this larger BC to slow the engine between 2 and 3 volts based on several past posts on smoke unit improvement.  At present, both smoke and whistle operate anemically at maximum 11 volts operating speed. If I increase the transformer to improve both, the engine will fly off the tracks. I even took your recommendation and installed a 20-ohm smoke resistor from Digi-Key.  It helped but the whistle remains weak at present operating voltage. Again, thank you.

The capacity of the bridge won't change the voltage drop, it just makes the part bigger for no gain in functionality.

Thank you again.  Great , I have a few 3A rectifiers and will use them on this application. 

Try them under a big load, check for diode heat every so often, then go larger if you'd like them a tad cooler. I've got 4a on one 6a on another 6 driver, they still warm the shells edges there good, but it is worse on the tiny ones

If you have a 2026 that  is overloading a 3A diode bridge, the engine has a problem!  3A is the continuous rating of the bridge, that would be way over what the motor should draw.

Thank you both for the excellent guidance. 

Not overloading, but plenty hotter than 4s. Most of my post war steam pulls right near 3a continuous. I have a few with 5.5a peaks for a second under heavy starts etc.  They will trip 80w modern breakers all day and eventually shut down a 1033 after a few hours. Been like that for 40 years on the 1033s. Use the KW; no issue.  I don't even have a pulmore Berk or twin pullmore,.or Type 1 monsters

6 driver steam with type 2 frame motors.

 sure the draw could drop with bearings etc. but they aren't screaming, locking, or sheading dust yet  . 

Heat is heat and doesn't vary, I know. The bulk helps dissipation with area.

You are so right.  I suspect my 2026 will continue to run smooth after the addition of the 3A BC but I will report the results here when available.  As you all know, there is plenty of room in the cab of a 2026 to add one or two BC's for the slowing factor.  We shall see soon.  Many thanks as always.