Existing decoder board can be snipped and has holes to solder wires from new decoder, but no plug.

I see no replies, and I am no model train expert, so I will step in the puddle.  How do you convert an H0 45 Ton diesel model to an ON30 model without using a new body? I thought the only thing common between ON30 and H0 was the wheels/trucks?  In any event adding sound to 45 Ton Bachmann Switcher is possible using existing speaker mount and a very small replacement decoder, but even then wires and decoder are squished.

Remove couplers and four small screws at corner of cab.  Entire top shell comes off. Couplers and shell are all tight fits.

On at least some Soundtraxx based Sound Value decoders, there is an auto start sound option, I think at cv 198.  And you can interlock sound with movement.  I know it exists on EMD F7A.

Looks great.  I am curious what you used for the numbers?  Decals?

This is a very interesting topic for me as a 57 year old.  My interest in model railroading has 2 bases.  My mother gave my father an American Flyer S set about when I was born, and as I grew up I remember my father occasionally trying to get the transformer, the switches, and the locomotives to work reliably.  I really enjoyed those times and the trains, even if my father did get  frustrated and angry often.  Together with that, I remember seeing an awesome layout at Disneyland at the entrance to Tomorrowland, if I recall correctly.  Although long gone, that layout remains in  my brain as awesome, something to play with, recreate, improve, and customize.  

As I approach retirement age, my plan is to create my own Pasadena Gulf Coast Railroad layout (in the rec room currently occupied by two Xboxes) in hopes that my grandchildren will enjoy it.  

The reason for saying all that is that I think the future of railroading is not necessarily in the iPhone/minecraft generation, but probably more likely in their children.  However you can expose the toddlers or crawlers today to a model train is how I think the future of our hobby will be secured. My granddaughter really loved the Polar Express train I set up last Christmas and I hope she and her cousins appreciate the future plans for Christmas trains.

If the elderly expose the young to trains, that is the place to donate the train.  If there is a better place to expose the 1-8 year olds, that is the place to donate the trains.

Great.  Thank you.  Wish my fingers were smaller that wire is tough to handle.

Got it, I think.  Thanks.  Attached is picture.

Thanks for the link to Shapeways.  Changing stack is on my todo list.  I. Have not been able to upload the picture of the tender; message says upload folder is full and I have no idea how to contact the administrator. Decoder is a flat board, slightly larger than the main board, mounted directly on top of the main board and screwed to it.  Speaker appears to extend through a hole in the bottom board. Will post picture when able. It is unlike the other Bachmann or the links to various 4-4-0'sound conversions and upgrades shown in this thread and elsewhere that I have seen.

Thanks very much.  That is a nicely done locomotive.  I am planning to look at mine again this weekend, still.  Been tied up with other issues.  I actually have three similar sound value Bachmann locomotives to compare; this one, a Jupiter (60), and a 119, all of which I plan, someday, to upgrade the decoder on (they currently sound identical - would be nice to tweak a little to make different).  It will be interesting to see how the tenders differ, since they were bought at different times. Will take photo of each tender.

Will open tender, take another look, and upload pictures this following week, probably next Sunday.  I know the tender is different from 4-4-0 Modern 80102 I have, which had an 8 pin NMRA socket on main board and Bachmann plug in decoder (no sound).  I think the 52705 has NEM 21 pin boards, from my quick look a couple of days ago.

Not a big fan of the three available whistles and would like to adjust the dimming levels. 

That is what I was afraid of. I installed a Tsunami2 Steam TSU-1100 in another locomotive of mine, but was hoping for something simpler to do this time. I will open it again and consider options.  Any input would be appreciated on alternative decoders, era 1865-1880.

Do Tsunami2 or Econami 21 pin PNEM decoders directly plug in to replace Bachmann's sound value decoders in the tender?  Thanks.