What I have is, is a MPC (about 1981) Chicago and Alton 4-6-4 with a electronic whistle and SOS. The original sound board has gone bad and no longer available. This used a trigger switch on the tender for the SOS contacts. I am replacing the bad board with Lionel's next generation SOS and whistle board. (8215-T15) which does not use make and break contacts for the SOS, but measures back efm from the motor for the SOS. My problem is the whistle is extremely distorted when the engine is running, but when the armature is not spinning the whistle is fine. The problem seems to be electrical noise from the armature. I tried the capacitors that are used on later engine brushplates, but that cancels out the SOS signal. What do I need to do to get rid of the electrical noise.
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