I'm putting together a AA964 Princeton from stuff on hand, and I have 3 unused 25uf/25v Sprague's, the old cardboard tube style. Any thoughts on using them? A buddy gave me stash of carbon comp resistors in just about every value, and I came across these and some other NOS caps. Thought it would be cool to keep the build "old school"
Thanks,
Mark
NOS Electrolytics
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NOS Electrolytics
"- Yeah, can we have everything louder than everything else? Right!"- Ian Gillan
Re: NOS Electrolytics
Meter them with an ohm meter as a basic good bad test should be over 15k ohms to be possibly good.
It's a start. The next test takes equipment.
It's a start. The next test takes equipment.
My Daughter Build Stone Henge
Re: NOS Electrolytics
You can try reforming them.
either in an amp or on the bench.
I know the Marshall guys like to reform the LCR and Hunts caps by first submerging them in hot water to help decrystalize the paste inside.
But with the paper tubes on yours, probably isn't a great idea.
Here is an article I saved about forming caps.
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 figure 6). As the capacitor reforms, the voltage across the resistor will drop (measured at the Xs in Figure 6). If that voltage will not drop below 10% of applied voltage after one hour, the capacitor is probably beyond help
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.
The electrolytics appearing on the surplus market have often been in storage for a very long period indeed. Some manufacturers use a visible code, of which the first two digits indicate the year of manufacture.
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!
Within an aluminum electrolytic there is a large area of aluminum foil and an electrolytic paste. As the voltage is applied, current flows until aluminum oxide forms on the surface of the foil, because aluminum oxide is a very good insulator. If excess voltage has been applied during the electrolytics lifetime, it is possible that tiny welds exist which the oxide insulator cannot separate. When that occurs, the capacitor cannot "reform", and should be discarded.
If the amount of current flow (voltage drop across the resistor) is great initially, that is not a problem. If it doesn't start dropping within five minutes of application of voltage, a definite hazard exists. The current flow indicated that energy is being dissipated within the capacitor, in the form of heat. Excess heat may "pop" the electrolytic, causing the paste to spit out...a threat to eyes and paint.
It's also worth remembering (one forgets only once) that a good capacitor will store its energy for quite a while, and discharge it through the hand when picked up. It's smart, then, to discharge the unit deliberately, through a resistor equal to about one ohm per volt of charge.
A new capacitor should rapidly take a charge right to rated voltage, in which case only a small voltage drop will appear across the resistor. It is possible to reform capacitors in the circuit, of course, but if rectification is by solid state diodes and there is a large current flow, it is possible to destroy one or more of the diodes, or to damage the transformer.
Electrolytic capacitors can be dangerous. They can be charged to a high voltage and will retain that energy for quite a while. If the terminals of associated circuitry are touched, a severe shock and burn may result.
Another hazard associated with electrolytics is "spitting". Each of these cans is filled with, among other things, a thick fluid which can be extremely irritating. A small rubber safety plug is fitted to most electrolytics of recent manufacture. When the capacitor fails, internal pressure may go too high; the plug will blow and the fluid will spit out.
Electrolytic capacitors of a given capacity and voltage will vary considerably in configuration and size, from one manufacturer to the another. Ideally, there will be chassis space to permit mounting the "twist-lock" variety. Otherwise, the tubulars (such as the Sprague TVL 1720) must be packed, glued or clipped wherever space is available.
The below drawing shows a 30K resistor but the guys at Metro use a 100K.
Not sure what difference it makes.
either in an amp or on the bench.
I know the Marshall guys like to reform the LCR and Hunts caps by first submerging them in hot water to help decrystalize the paste inside.
But with the paper tubes on yours, probably isn't a great idea.
Here is an article I saved about forming caps.
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 figure 6). As the capacitor reforms, the voltage across the resistor will drop (measured at the Xs in Figure 6). If that voltage will not drop below 10% of applied voltage after one hour, the capacitor is probably beyond help
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.
The electrolytics appearing on the surplus market have often been in storage for a very long period indeed. Some manufacturers use a visible code, of which the first two digits indicate the year of manufacture.
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!
Within an aluminum electrolytic there is a large area of aluminum foil and an electrolytic paste. As the voltage is applied, current flows until aluminum oxide forms on the surface of the foil, because aluminum oxide is a very good insulator. If excess voltage has been applied during the electrolytics lifetime, it is possible that tiny welds exist which the oxide insulator cannot separate. When that occurs, the capacitor cannot "reform", and should be discarded.
If the amount of current flow (voltage drop across the resistor) is great initially, that is not a problem. If it doesn't start dropping within five minutes of application of voltage, a definite hazard exists. The current flow indicated that energy is being dissipated within the capacitor, in the form of heat. Excess heat may "pop" the electrolytic, causing the paste to spit out...a threat to eyes and paint.
It's also worth remembering (one forgets only once) that a good capacitor will store its energy for quite a while, and discharge it through the hand when picked up. It's smart, then, to discharge the unit deliberately, through a resistor equal to about one ohm per volt of charge.
A new capacitor should rapidly take a charge right to rated voltage, in which case only a small voltage drop will appear across the resistor. It is possible to reform capacitors in the circuit, of course, but if rectification is by solid state diodes and there is a large current flow, it is possible to destroy one or more of the diodes, or to damage the transformer.
Electrolytic capacitors can be dangerous. They can be charged to a high voltage and will retain that energy for quite a while. If the terminals of associated circuitry are touched, a severe shock and burn may result.
Another hazard associated with electrolytics is "spitting". Each of these cans is filled with, among other things, a thick fluid which can be extremely irritating. A small rubber safety plug is fitted to most electrolytics of recent manufacture. When the capacitor fails, internal pressure may go too high; the plug will blow and the fluid will spit out.
Electrolytic capacitors of a given capacity and voltage will vary considerably in configuration and size, from one manufacturer to the another. Ideally, there will be chassis space to permit mounting the "twist-lock" variety. Otherwise, the tubulars (such as the Sprague TVL 1720) must be packed, glued or clipped wherever space is available.
The below drawing shows a 30K resistor but the guys at Metro use a 100K.
Not sure what difference it makes.
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Tom
Don't let that smoke out!
Don't let that smoke out!