[Milsurplus] Rebecca Eureka Dynamotor

[Brad Latta]

I have a dynamotor here that puts out 80v a.c. @ 2kHz , input is 28V d.c.
 Initially due to surface corrosion, the shaft was frozen, but I have managed to clean the rust out & free the shaft by dissasembly. I have now powered up the dynamotor, & I find that with 4.3V d.c. on the field it outputs the 80V into a 60W incandescent globe ( A 5uF series capacitor is required on the AC output winding ). In the aircraft a carbon pile regulator is used to regulate the D.C. voltage on the field. As I don't have a carbon pile regulator, I'd like to use an op amp circuit to regulate the field.
Anyone ever done this before? I imagine I'll have to rectify the 80V output & feed it into an op amp circuit with a reference voltage, the output voltage adjusting the field. 
                               Brad