Can anybody suggest a source and part number for something like this to use on a conventional powered engine?
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How much current do you need at 6 volts, and does it have to be exactly 6 volts, & regulated?
Are you talking for something like lights inside the locomotive or something to actually run the locomotive? Inside for lights, etc. I use something like this. If you bolt the heatsink to the frame, you can get around 100ma or more out of this, 40-50ma if you just heatshrink it.
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Yes...lights inside a locomotive.
Leds...John what are the details on that board?
Which kind of leads to another question since John mentioned it...
If you had a regulated power supply with enough amperage capability...would it in fact act like a cruise control?
Say...crank the power supply to 18 volts...regulate it down to 10 so that the engine always sees 10 volts...on a flat with no grade speed would be constant...yes?
Then...you add a pot on the board to dial in your speed (voltage)...and cruise...maybe...
@gibson man posted:Which kind of leads to another question since John mentioned it...
If you had a regulated power supply with enough amperage capability...would it in fact act like a cruise control?
Say...crank the power supply to 18 volts...regulate it down to 10 so that the engine always sees 10 volts...on a flat with no grade speed would be constant...yes?
Then...you add a pot on the board to dial in your speed (voltage)...and cruise...maybe...
No, that wouldn't work. It would simply supply a constant output voltage, however with varying loads on the locomotive, you really need varying voltage to adjust the torque of the motor to the load conditions.
Think about it, with good track wiring, you already have constant motor voltage at a single transformer setting for a simple conventional locomotive.
@gibson man posted:Yes...lights inside a locomotive.
Leds...John what are the details on that board?
I make them. They have an LM78xxT regulator and input circuitry to rectify and filter the incoming track power. They also include a 22uh inductor for MTH DCS compatibility. I use them in locomotives all the time for a number of tasks, wherever I need a small source of DC power from track voltage. As I said, in free air, count on 40-50ma of power. If you bolt the heatsink to the chassis, you can easily get 100ma or more.
Well John...the reason I asked that question is because of what I see running conventional trains.
Seems like higher voltages at some point overcome resistance in the track...like, say across track joiners in fastrack...such that at low voltages pulling power straight from the track you hit those high resistance spots the train slows...but at higher voltages that effect seems to diminish.
My logic is that at higher voltage the resistance is reduced...and then by regulating down your engine would always see a solid voltage and run more consistently...and not necessarily require intensive wiring schemes to get more consistent operation.
Just a thought...
Actually, the voltage on the track doesn't change the characteristics of a high resistance joint. The higher voltage just has makes the voltage drop less noticeable.
If you have a 1 ohm resistance at a joint, and you're running 6V on the track at a one amp load, you're losing about 16% of your voltage through the joint. However, if you're running 12V on the track at that same one ohm load, you're only losing about 8% of the voltage across the same joint. Obviously, this will have a lesser effect on running.
I guess what I mean to say is...'at higher voltages resistance is OVERCOME...'
Well, yes. However, if you have a joint with high enough resistance to be a factor at any voltage, it's only going to get worse over time. If a single track joint is causing any noticeable operational issues, it should be addressed. A high resistance joint can also get very hot under load, occasionally hot enough to potentially start a fire.
But...also...I'm running on a 10x4 table...and checking the track voltage directly my engine runs best at say 11 volts...reasonable speed...maybe a little faster than I'd like...but anyway...when that engine crosses a track joint at one location the measured voltage drops by .4 volts...10.6 volts then...and this small drop is enough to almost stop the train...thus why I asked about strictly regulating power inside the engine with just a simple regulator for conventional operation.
Regulating power inside the engine is treating the symptom, not the disease.
Fix the track joint or add another power feed to the track.
Regulating the power inside the engine is known as cruise control. 
However Rich is right, fix the track.
When I first laid my track for my new layout, I did a quick test by connecting power at one point on the 12 x 24 layout and running an engine around the whole layout. I had no issues running, though when I actually measured the voltage at the far end under a 2A load, they varied about a volt and a half from the connected transformer voltage, not bad for all that track and joints.
FWIW, I now have probably at least 75-80 power drops around the whole layout with 500 feet of track in total.
Hard to believe dropping from 11 to 10.4 is enough to stop the train. I'd also look out outside rail continuity on both sides.
Another thought, where are you reading the voltage and where is the spot the loco almost stops? If reading the .6 volt drop at the transformer, you could have a much bigger drop at the track in question pointing to other issues. A short or low resistance 20 feet away turns the whole track to a heating element when you crank up the juice.
You could also read the 10.4 with a meter and still have 0 volts when a load is applied on a bad track joint.
So it drops that .6 volts crossing a joint probably 15/20 inches from power drop...then as circles around the track along another 20/30 inch section it creeps upward...then hits another joint...starts creeping back up as voltage goes up as it comes back around to the drop.
All the engines see this and respondsimilarly...even my older lionmaster engines (although not so much).
It's like 10.5-11 volts is verging on stall versus running flat out (load depending)...
Your probably all correct i just need to add drops...but was wondering if there was an easier way on a smaller layout.
@gibson man posted:...but was wondering if there was an easier way on a smaller layout.
This would be easier than adding power drops and as many others have already suggested, a great place to start..
