An ESR ( Equivalent Series Resistance ) meter is a practical device to locate and test faulty electrolytic capactors. This can be done 'in circuit' , but of course also to test salvaged capacitors before you build them in. If the elco's istart breaking down their internal resistance becomes too high. Ordinary multimeters are for this type of measuremet useless. ESR-meters use a high testing frequency to conduct this measurement.
Vintage Novanex amps still work mostly without problems even after 40 years. Novanex only uses top quality components and state of the art production equipment. Some series of Philips Elco's over 40 year old seem to breakdown prematurely. Sometimes faulty electrolytes are easy to distinguish sometimes not. In that case our ESR are the perfect tool. The Blue Line ESR-meter can also be used to test rechargeable batteries and accumulators op till a voltage of 24 Volts.