These came to us as part of a lot of surplus stock from a large Milspec type OEM and have been kept in storage for some years, they to are date coded 7909, MEANING 1970 WEEK 9 we have therefore classified them as ‘new other’. They are however in serviceable condition providing they are reformed.

ITT –  International Telephone & Telegraph are a US based manufacturing Co. They produced components for the aerospace, transportation, energy and industrial markets and had a reputation for high quality and reliability. These capacitors are of that ilk, ideal if your project requires hi end components.

Please Note! Having been manufactured in 1979 these capacitors will almost certainly need reforming. The process of reforming an old aluminum electrolytic capacitor consists of the application of rated voltage, through a resistor, for a period equal to five minutes plus one minute per month of storage.

These capacitors are intended for sale to competent electronic engineers, like all electronic components considerable knowledge and skill is required when using them.

PLEASE DO NOT PURCHASE UNLESS YOU MEET THIS CRITERIA!

Reforming Electrolytic Capacitors

Manufacturers claim that most old electrolytics can be saved if the correct procedure is followed, regardless of how long they have been unused. Such capacitors must be “reformed”. This process consists of applying rated voltage through a resistance (about 30,000 ohms, five watt) for five minutes plus one minute for each month of storage (see diagram below). As the capacitor reforms, the voltage across the resistor will drop (measured at the Xs). If that voltage will not drop below 10% of applied voltage after one hour, the capacitor is probably beyond help.

The circuit shown in the sketch above works reasonably well. Apply the rated voltage through a 5W resistor. Anything from 20K-50K will do, as this is far from a precision process. The meter is used to measure the voltage drop across the resistor; when no current is flowing, there will be no drop. Obviously, when there is a large voltage drop (more than 20% of the applied voltage), there must be a significant current flow through the capacitor. The nature of a proper capacitor is to impede DC current flow, so when there is such flow, something must be wrong.

Note: Apply the appropriate D.C. voltage to the capacitor with a D.C. power supply. An old Kepco, Lamba etc. tube regulated lab power supply rig works great. Be sure to observe the proper polarity!