LGB F7 B unit

Typically B units were run in conjunction with an A unit, and effectively permanently coupled together, while providing control of the B-unit, from the A unit, this was done to increase the pulling power.  The main differences between an A and B units are that B  didn’t have a crew cab, to operate the locomotive from. However, B units do actually have a front and back, along with the porthole windows on the side. the windows served a couple of purposes, to let light in, as well as provide a window to move the B unit around within a yard.  The B units like the A units had a steam generator as well as an electrical box.   and finally internal lights, to allow the breakman the ability to see what they were doing inside.


I’m not sure if I mentioned this in the post about the F7’s in general, in working with the B unit, from the limited edition set from LGB


The B unit had an analog sound card and wasn’t powered.  This, provided a huge issue for the A unit when attempting to pull its train up a grade, and unfortunately, it only has one traction tire.

after some discussion and ideas, we originally thought about just upgrading the A unit, to DCC, and adding weight. with the best option to add power to the B unit.

this brought up some new challenges and several ideas:

With the 1st thing being to upgrading the unit to power trucks, and adding weight, as before it was just a plastic shell on wheels.

Then came the question how to power those trucks?  here’s where some of the fun starts:

  • running a high amp decoder, then connecting motors, and a speaker from the A unit to the B unit.
  • doing a dual decoder install?  pulling power and sound from the A unit for the second decoder
  • setting up a no sound decoder for the B unit, pulling the sound from the A unit.  and running them in a consist.

and here was the final idea, after upgrading the power trucks, and finding the sound project for the B unit. I decided to add a Sound Decoder and treat the unit as its own locomotive.  and because I felt it a waste to not use at least 1 of the lighting output from the decoder I added lights.

here’s the B unit, with its lights on, and a photo of the light bar, during testing.



Some different options and ideas for the light bar, I played with using LED strip lighting, purchasing an LGB light bar, or making one, I also considered different wiring options for the LEDs, for this project I played with using a CL2N3-G LED driver and running the LEDs in serial versus parallel to using resisters after playing and testing the ideas I finally settled on resistors in serial with the LEDs but set up in a parallel circuit, this gives me equal power distribution aka light output from each LED, it also doesn’t kill the whole string if a LED burns out.

Here’s a couple of pictures of the lightbar finished, and how it is installed in the B Unit, in this case, I chose to use the body supports, which are actually screwed to the chassis, they help support the body structure, and provided a perfect support system for the light bar it’s self.


Then finally, once both units are done, I’ll map the B units lights to turn on with the headlights of the A unit.

another neat feature, that I can do with Zimo decoders, is that I can have the cab light automatically dim or turn off when the locomotive starts moving, this is the primary reason for mapping the interior lights of the B unit to the headlights of the A unit.

the last tidbit is that I’m leaving the LGB loop couplers on the rear of the A unit, and the Front of the B unit, while the passenger cars and the rear of the B unit have been upgraded to use Kadee couplers. this designates the front and back of the B unit and ensures that the A and B unit is hooked up the same way each time.

All these features will bring the models to the next level, proving an experience that’ll be unique, while resolving the tractive issue of pulling the cars up the grade.

This is what I talk about in my pricing, by taking the extra mile.

here’s a video of the B unit under its own power for the 1st time.


here’s some photos of the finished install of the B-unit with the final weights and lights.



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