Monarch 10ee 4000rpm machine will not go over 1700 rpm.

I have a nice 10ee from the 60's that is a 4000 rpm machine but it will not go over 1700. I poked around on google and got many ideas but it would help to hear from someone who personally solved the problem. The machine is still all original with vacuum tubes.

MARK07747 said:

I have a nice 10ee from the 60's that is a 4000 rpm machine but it will not go over 1700. I poked around on google and got many ideas but it would help to hear from someone who personally solved the problem. The machine is still all original with vacuum tubes.

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Is it in Back gear?


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The speed pot is bad. Custom item from Monarch. It's been discussed here.

No, it is not in back gear. Is there a way to test the speed pot to be 100% sure? Thanks, Marc

MARK07747 said:

No, it is not in back gear. Is there a way to test the speed pot to be 100% sure? Thanks, Marc

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Put a voltmeter on the motor field terminals. As you bring the speed up from minimum, the field voltage should be about 120 volts DC until you reach base speed, around the 1700 RPM you are seeing. At that point the armature voltage should be about 240 VDC and stay there the rest of the way. From there the speed increase is accomplished by reducing the field voltage, known as "field weakening". It is likely that your field voltage will not decrease. For a quick check, watch the C3J thyratron glow. If it doesn't change as you move the speed pot, the problem is from the tube back to the pot. The pot has two sections, one controlling the armature voltage and the other the field. Each section has three terminals, the one in the middle being the moving wiper. Connect a voltmeter to a center terminal and one of the outer ones on that section. If the voltage changes during the first half of the range, you are on the armature pot. Switch to the other section and see if the voltage changes in the second half of rotation. If it does, the pot is good and you need to look for the failure elsewhere.

Bill

Many thanks, Bill! I will try that out asap.