REVENUE - Disaggregation of Revenue (Details) - USD ($)	12 Months Ended
	Apr. 30, 2019	Apr. 30, 2018
Disaggregation of Revenue
Net sales	$ 20,555,000	$ 18,396,000
Domestic
Disaggregation of Revenue
Net sales	18,472,000	16,237,000
Foreign
Disaggregation of Revenue
Net sales	2,083,000	2,159,000
Commercial Aerospace
Disaggregation of Revenue
Net sales	7,690,000	7,830,000
Defense
Disaggregation of Revenue
Net sales	11,849,000	9,611,000
Industrial
Disaggregation of Revenue
Net sales	1,016,000	955,000
Magnetic components
Disaggregation of Revenue
Net sales	10,600,000	9,251,000
Potted coil assembly
Disaggregation of Revenue
Net sales	5,751,000	5,962,000
Electro-mechanical assemblies
Disaggregation of Revenue
Net sales	3,920,000	3,060,000
Large transformers
Disaggregation of Revenue
Net sales	284,000	$ 123,000
Balances Without Adoption of ASC 606
Disaggregation of Revenue
Net sales	19,451,000
Balances Without Adoption of ASC 606 | Domestic
Disaggregation of Revenue
Net sales	17,392,000
Balances Without Adoption of ASC 606 | Foreign
Disaggregation of Revenue
Net sales	2,059,000
Balances Without Adoption of ASC 606 | Commercial Aerospace
Disaggregation of Revenue
Net sales	7,616,000
Balances Without Adoption of ASC 606 | Defense
Disaggregation of Revenue
Net sales	10,822,000
Balances Without Adoption of ASC 606 | Industrial
Disaggregation of Revenue
Net sales	1,013,000
Balances Without Adoption of ASC 606 | Magnetic components
Disaggregation of Revenue
Net sales	10,197,000
Balances Without Adoption of ASC 606 | Potted coil assembly
Disaggregation of Revenue
Net sales	5,094,000
Balances Without Adoption of ASC 606 | Electro-mechanical assemblies
Disaggregation of Revenue
Net sales	3,876,000
Balances Without Adoption of ASC 606 | Large transformers
Disaggregation of Revenue
Net sales	284,000
Effect of Change Higher/(Lower)
Disaggregation of Revenue
Net sales	1,104,000
Effect of Change Higher/(Lower) | Domestic
Disaggregation of Revenue
Net sales	1,080,000
Effect of Change Higher/(Lower) | Foreign
Disaggregation of Revenue
Net sales	24,000
Effect of Change Higher/(Lower) | Commercial Aerospace
Disaggregation of Revenue
Net sales	74,000
Effect of Change Higher/(Lower) | Defense
Disaggregation of Revenue
Net sales	1,027,000
Effect of Change Higher/(Lower) | Industrial
Disaggregation of Revenue
Net sales	3,000
Effect of Change Higher/(Lower) | Magnetic components
Disaggregation of Revenue
Net sales	403,000
Effect of Change Higher/(Lower) | Potted coil assembly
Disaggregation of Revenue
Net sales	657,000
Effect of Change Higher/(Lower) | Electro-mechanical assemblies
Disaggregation of Revenue
Net sales	$ 44,000