Converting DC locos to DCC is not about a specific locomotive or a specific decoder. It is about how much space you have or are willing to make inside the locomotive shell.
Then, measure the available space or make a small block for a test fit. Once you have the dimensions of the space, then choose a decoder. You can hard wire in a decoder directly or install a wiring harness first, then plug in a decoder. The only electrical parameter you must consider is the maximum stall current under DC. You must select a decoder with the same or higher stall rating as the motor. So you do not overload the decoder.
What Should I Do With All My DC Locomotives?
(I Can't Afford to Convert All My DCC Locomotives)
Those that switch to DCC from a traditional DC layout and have a fleet of DC locomotives often contemplate a layout that combines DC and DCC. The fear is that you can't afford to convert all those locomotives. Don't worry about it. Go ahead and jump into DCC! There are some good reasons.
I will start with the bad news. Mixing DC and DCC can be fatal to your DCC electronics. If a locomotive crosses a gap between a segment on DCC and another on DC, it could fry things. If you have a crossing with one side DC and the other DCC, and a locomotive derails on it, smoke could be the result! For more on this topic, see the section on using DC and DCC on the same layout.
Even if coming up with $20 for a decoder is a problem for you and the total cost seems frightening, relax. You will probably be more pressed for time to install decoders rather than paying for them.
Converting old locomotives can take a tremendous amount of time, especially if the locomotive has a metal frame and the motor and power pick-ups are not isolated from the frame. Most old locomotives are like this. If you have a brass locomotive, you can guarantee this is the case.
Also, old locomotives probably have very few wheels picking up power. So besides isolating the motor, you may have to add power pickups.
Finally, the motors in old locomotives were not usually of high quality. So you may find yourself needing to replace the motor, too.
I still have a large fleet of old DC locomotives. A few I will convert to DCC if I ever find the time. The rest will sit on the shelf, making it like a museum piece. Orr, I will sell them on eBay to someone who can't pass up a great deal and has loads of time to convert them to DCC. Hint If you see a deal on eBay, be sure to inquire if it is DCC-ready. Otherwise, that deal may end up costing you a lot of time and money in the end.
Save your pennies and buy a few modern, quality locomotives that run well. Even if they don't come with a DCC decoder, DCC-ready locomotives won't take much work. They also look much better than those of yesteryear. You will be much happier.
Don Vollrath's thoughts:
Conversion of old locos is not necessarily as easy or as rewarding as you might think. It can be a lot of fiddling around, time-consuming, and somewhat disappointing. But once you take the plunge and buy a decent RTR (ready-to-run) loco, especially with sound, there is instant gratification. Like Allan, I've got plenty of what used to be favorite DC locos yet to be converted. The older tooling can look toy-like compared to the latest models. The open-style motors draw too much current. They seemingly "ran great" on DC... but not when compared to today's standards. They sit on unpowered stall tracks or are stored in boxes alongside the other numerous yet-to-be-built kits. [I've got a pre-DCC Atlas GP40 on my workbench right now and am struggling in my 'spare time' with how to mount the Tsunami decoder and speaker.]
One good option for the novice is to have a knowledgeable local club member or friend help with the first couple of decoder installs. But yet, there is a big jump from the $69 RTR DC GPxx, or a $100 around-the-tree train set, to the multi-hundred dollars it takes to get started in DCC. Selling old stuff at a swap meet isn't very productive, as the guys that go there are not that interested in old treasures. One option I have taken is to give several old DC locos with a power pack and track to interested neighbor kids.
Mark Gurries' thoughts:
Modern DCC-ready locomotives have state-of-the-art better detail, paint jobs, mechanical design, electrical pickup, and lighting systems. DCC versions often include sound, giving you a whole new dimension to your layout enjoyment. If one combines the locomotive budget with the DCC decoder budget, one will often get a much more rewarding experience the day you buy it and place it on the layout the same day and run it. This is your best option if you find yourself electrically challenged.
If you cannot afford a locomotive upgrade path and you want to convert some old locomotives to DCC, start by only converting your two favorite locomotives. Do not attempt to convert them all at once. Once you have done these, you have a better idea of what the best thing might be going forward with respect to the rest of the old fleet.