NMRA British Region Forum

TCS decoders are quite good, and this one has the 'keep alive technology'. While I haven't got one with that option myself (I've used T4X decoders) , it should otherwise be a good decoder. The only draw back is that you can't really 'tune' the BEMF, it can only be switched on or off, and the decoders are supposed to 'learn' and adjust themselves. This can be a bit hit and miss, and you'd need a smooth running loco, that performs well on DC too. (Atlas should be a safe bet), I've had some old Athearn BB locos that were very hard to get right, but others worked fine.

The keep alive technology makes the whole decoder a bit bigger and more difficult to get under the hood though, but I don't think it's a huge problem.

Koos

I've a pair of 'KA' series ones (can't recall which at the mo) in my 90macs, they are a good decoder and the KA element works very well although I'm planning to move them into a pair of SW1500s shortly where their skills may be more useful - I don't think you'll have a space issue in the GP39s

Been messing about with decoders tonight, my pair are also KAT12s and I can confirm they fit my Trainman GP38-2, so unless Atlas have done something weird on the GP39-2 you should be fine.