GP-40 dcc conversion help

[baldwinmikado]

ive got 2 bachmann gp-40 dc locomotives. on is AT&SF and the other is Western Maryland. they are standard dc. i would like to add sound and dcc and i am currently thinking about MRC's decoder for 645E prime mover locomotives. is any one aware of a decoder or manufacturer that makes decoders w/ gp40 sounds and how is the decoder from mrc. i am working on a budget so a 100+ dollar chip is a little to much.

[bapguy]

I would go with the MRC decoder # 1619. MicroMark has them listed at $51.95. The bigges prblem is making sure you have room for a decoder. You need to know the clearence between the top of the frame and inside top of the shell.  Contact MRC to see if you can get the dimentions on this decoder to see if it will fit. Also what size speaker comes with it. Speaker location can be a problem as well. You might fit a small speaker on the rear of the frame where it steps down. I added sound to a GP30 and put the speaker (.63" diameter) there. If you want to use LED's which I recommend, you need a 1K resitor  between the decoder and one side of the LED's leads. Joe

[baldwinmikado]

Thanks. i checked with mrc, the decoder is $72.98 not including tax or shipping. i found the online manual for the decoder, it say that an 18 to 28 mm speaker is recommended. it also says that an 18mm speaker can fit on the decoder. It aslo gave me the specs for the decoder on the first page. 73mm x 17.8mm x 7.7mm. Thank you for the reference and the location of the cheaper decoder.

[baldwinmikado]

one more thing every body, i have seen a few videos of how important resistors are with this loco. if i use the factory light bulb, will a resistor be necessary, or will i just have to use an led, and if so what size and kind.

[bapguy]

If you read the decoder manual, I believe it states the light out put is 12 Volts. Remember, bulbs create heat which can melt or distort plastic shells if the bulbs are too close. That is why I use LEDS with a resister. No heat from LEDs.  Joe

[richg]

If you read the decoder manual, I believe it states the light out put is 12 Volts. Remember, bulbs create heat which can melt or distort plastic shells if the bulbs are too close. That is why I use LEDS with a resister. No heat from LEDs.  Joe

Twelve volt bulbs never get to twelve volts in DC locos. Those that do find their loco on the floor.
As was said, the bulb will always get twelve volts with DCC. Those bulbs get quite hot.
Some use 1.5 volt bulbs and a resistor. Those run much cooler and some think they look more prototypical if you count rivets.
A couple companies sell a sound decoder with outputs for 1.5 volt bulbs and 12 volt bulbs.
Some use LED's and a 1k resistor but not on the 1.5 volt terminals, only the twelve volt terminals.
A couple companies sell a sound decoder that is ready for LED's. The resistors are on the board.

Do some more research. Much of DCC is not plug and play.

https://sites.google.com/site/markgurries/home/part-sources/led-s/resistors-for-leds-bulbs

Rich