Thanks for the info on Dallee. I'd forgotten about them, and I think that might be easier.
Regarding the DC offset, no I don't know how they detect it on this tender. There are a number of circuit cards stacked in the tender and I don't have a schematic. One circuit card is dedicated to the reversing circuitry and there is an amplifier board for the sound. I literally just started looking at it a day ago. I'm inclined to leave it intact and set it aside then do my own sound if I elect to go that route.
Thanks again to all that have replied!