REVENUE - Disaggregation of Revenue (Details) - USD ($)	3 Months Ended		6 Months Ended
	Oct. 31, 2019	Oct. 31, 2018	Oct. 31, 2019	Oct. 31, 2018
Disaggregation of Revenue
Net sales	$ 6,792,000	$ 4,874,000	$ 13,138,000	$ 9,347,000
Domestic
Disaggregation of Revenue
Net sales	6,586,000	4,501,000	12,684,000	8,655,000
Foreign
Disaggregation of Revenue
Net sales	206,000	373,000	454,000	692,000
Commercial Aerospace
Disaggregation of Revenue
Net sales	2,749,000	2,637,000	5,159,000	4,743,000
Defense
Disaggregation of Revenue
Net sales	3,874,000	2,055,000	7,697,000	4,124,000
Industrial
Disaggregation of Revenue
Net sales	169,000	182,000	282,000	480,000
Magnetic components
Disaggregation of Revenue
Net sales	3,910,000	2,386,000	7,164,000	4,543,000
Potted coil assembly
Disaggregation of Revenue
Net sales	1,408,000	1,586,000	2,927,000	2,865,000
Electro-mechanical assemblies
Disaggregation of Revenue
Net sales	$ 1,474,000	$ 902,000	$ 3,047,000	1,659,000
Large transformers
Disaggregation of Revenue
Net sales				$ 280,000