REVENUE - Disaggregation of Revenue (Details) - USD ($)	12 Months Ended
	Apr. 30, 2020	Apr. 30, 2019
Disaggregation of Revenue
Net sales	$ 26,133,000	$ 20,555,000
Domestic
Disaggregation of Revenue
Net sales	25,082,000	18,472,000
Foreign
Disaggregation of Revenue
Net sales	1,051,000	2,083,000
Commercial Aerospace
Disaggregation of Revenue
Net sales	10,208,000	7,690,000
Defense
Disaggregation of Revenue
Net sales	15,140,000	11,849,000
Industrial
Disaggregation of Revenue
Net sales	785,000	1,016,000
Magnetic components
Disaggregation of Revenue
Net sales	14,090,000	10,600,000
Potted coil assembly
Disaggregation of Revenue
Net sales	5,655,000	5,751,000
Electro-mechanical assemblies
Disaggregation of Revenue
Net sales	$ 6,388,000	3,920,000
Large transformers
Disaggregation of Revenue
Net sales		$ 284,000