Bachmann 'LYN' type loco

Tim,
 
The MyLocoSound steam soundcard will certainly do the job. A friend of mine has asked me to install one in his Bachmann Lyn and I am due to pick it up this weekend. The conversion I am doing is much bigger than you will need to do because he wants to change it to battery power radio control using an Aristocraft Revolution controller.
 
In your case, you just need to install the soundcard (the cab floor looks a good place) and connect it to the existing wiring. Very little soldering needed. If you decide to order a soundcard, I will work out the connections for you.
 
When I have finished the conversion here I will post details and a video.
 
Regards
Peter Lucas
www.mylocosound.com