I have several old brass locos and they have Pittman motors.
I have tried DH163 Decoders and blown two.
I believe that they draw excess current that exceeds 1.5amp cont.
Is there an HO mobile decoder with the same size physically as DH series, but has higher current ratings? Suggestions?
While it is possible that the motor may be drawing too much current, it also may be possible that the motor brushes are not isolated from the frame of the locomotive.
It also would be helpful for you to determine the stall current of the locomotive to see if the engine is actually drawing higher current.
If there are no accidental electrical paths to the frame from the motor brushes and the stall current is inordinately high, your next options are more intensive.
For both Digitrax decoders, and also the decoders of other manufacturers, the industry standard for H0 sized decoders appears to be 1.5 Amp continuous and 2 Amp peak.
Given that fact, you have two approaches at your disposal, either replace the motor or make the locomotive's mechanism more efficient.
If motor conversion seems to be your path of choice, there are resources available to help.
I have talked with others about brass conversions and those who have the experience tell me that it is relatively easy.
Of course, it's easy because they have the experience, etc.
In looking at my modest collection of brass, most have open frame motors, but most also date back to the pre-DCC days of the 1980's and earlier.
I have several units which were imported by Fomras, units which were very smooth runners in the DC environment.
I have converted them to DCC, but even though they are single units that will pull no cars, there are still issues with the motors.
They need to be tweaked to get the start speeds correct.
And, I have several Suydam units, which were built by Orion in the 1960's with huge honking motors, that will need to be converted.
The conversion process involves removing the open frame motor and replacing it with a can-type.
There's a company called A-Line (Walthers manufacturer #116) which makes motor mount cradle weights for this use.
They offer other items for these conversions also.
Apparently the motor can be held in place with double stick tape or RTV resin.
You may be able to improve the performance of your locomotive, and thus lower the current consumption, by working on the locomotive mechanism itself, excluding the motor.
In looking at brass locomotives over the years, I have noticed one odd trend.
Many of these locomotives are not good runners because the builder felt that the locomotive would be only on display.
When you go back and look at the locomotive mechanism piece by piece, little odd errors show up from time to time.
A side rod hole may be drilled off center, or the drill hole not cleaned up, leaving a burr which increased the drive's resistance.
In the case of the burr, the so-called break-in period eventually wears this down and the locomotive begins to run more smoothly.
Ultimately, the solution to making any locomotive run better is to disassemble it and then rebuild it.
As you slowly reassemble it, test the drive by turning the wheels or pushing it down a section of track.
By testing in this manner, you will eventually add a part that causes the mechanism to move significantly tighter.
This will be the source of the drive's problems, and careful examination will show that something in the newly added part needs to be corrected.
And, as you continue, you may find other parts that need adjustment.
The last step is to add the motor, and by that time, you may have removed enough resistance that even the old Pittman may draw less current.
It is a slow process but one that gives you a very sweetly running locomotive in the end.