Converting MTH 2-rail GP-40 to DCC - specifically the bulbs

I would suggest converting them to LEDs so there's no heat from them.

The bulbs in the MTH Proto-2 engines are 6-volt Grain of Wheat. They get roughly five volts from the board. As Joe suggested, I'd recommend using LEDs with your DCC board instead of bulbs as they last longer, give more light, and don't produce heat. If it's a working Proto-2 board, remove it carefully from the locomotive and sell it. The 5-volt boards use an 8.4-volt rechargable battery; the 3-volt boards use a pair of 1.2-volt batteries in a shrink-wrap.

I was certainly thinking that if I blew the bulbs, my plan B would be to replace them with LEDs instead.  I guess I should take a look inside and see how hard that would be to do as a plan A.  6V is an odd number compared to other stuff I've done (in HO and N mostly) and probably isn't worth the hassle to me of working out what the proper resistor value should be.  I'd be so nervous I'd got the values wrong.

As I'm based in the UK, it's not that easy for me to sell the ProtoSound 2.0 board.  I certainly couldn't be confident enough in it to put it up for sale on eBay - the grief of returns/refunds to the purchaser across the Atlantic wouldn't be worth it if it turned out not to work.  I'll have to think about it.

Thanks for the advice.  I'll let you know how I get on - I have an HO scale layout to finish first which is due to be exhibited in like six weeks, so that's on a deadline.

Regards, Bevis.