can someone please tell me what digitrax decoder to use for the Bachmann Spectrum 82103 J Class 611?
First you need to determine the stall current of the locomotive, using a digital multimeter on a DC powered track. All my Bachmann locos have a stall current of less then .75 amp, but yours may be higher.
The Digitrax DH123P/PS is rated at 1.5 amp, the DZ123P, which is smaller, is rated at 1 amp, either one can be plugged into the 8 pin socket. I'm not familiar with the locomotive, you may have to clip the interference suppressor capacitors if they exist on the pc board. Others may comment on this requirement.
I use mostly DH123 and have been very pleased with the performance.
me too, the 123 should work very well in the J