conditioning electrolytics

[rounder]

hello, How do you condition your electrolytic caps? Most Variacs I've seen (on e-bay at least) go up to 140 Volts max. Several of my caps are 350 Volts. Also, how long do you let it sit on a voltage before you step up the voltage and how much do you step it up. I guess I'm asking for a tutorial on seasoning electrolytics.

Thanks,
Zig

[pdf64]

Why do you think you need to do this? It's only done usually on amps that haven't been powered up in a while.
Variacs are ac devices, whereas as electrolytics are polarised / dc. Connect them to a variac and they will eventually explode as the voltage is increased.
Normally the variac will feed an amp, the power supply in the amp will boost and rectify then feed the caps. Pete.

[Jazz P Bass]

Thanks Pete.
Man am I glad he didn't hook them up to a Variac.
Link: EEVblog #42 – Exploding Capacitors in High Speed @ EEVblog – The Electronics Engineering Video Blog
(compliments of Steve Conner)
As to the post, some "experts" recommend reconditioning electrolytic capacitors from old equipment.
The idea is to slowly (with the appropriate power supply) bring up the voltage over a certain amount of time.
This is supposed to help "reform" the insides of the cap.
What is not usually mentioned is what happens if the cap is all dried out.
It's called a short on the power supply.
It would probably be a good idea to underfuse the whole arraingement.

[madkatb]

I found this if it helps.
Reforming Electrolytic Capacitors
Seems to me that someone posted the same idea only using a light bulb limiter instead of the resistor and started with a low wattage bulb and worked up to higher wattage bulbs,. Maybe use a resistor too. Replace any tube rectifier with a pair of ss diodes strapped across the tube base and pull all the other tubes.
As the current draw fades to zero the light bulb eventually goes out.
It's handy cos you don't need to remove any components from the amp and if the light bulb never goes out you know you have a problem (without anything blowing up).

[J M Fahey]

Un-politically correct answer: if an electrolytic capacitor in your amplifier really *needs* reforming, drop it in the nearest junk can an replace it by a new one.
Sorry.

[Steve Conner]

Yes, it's like trying to "refresh" week-old sushi. You can get new replacement caps in vintage styles from the likes of F&T and CE Distribution.

It's commonly attempted by vintage radio enthusiasts who want to keep the piece as original as possible, though. If the capacitors were in a cool place inside the unit, sometimes they can be OK.

As other people pointed out, you need more than just a variac, you need a transformer and rectifier, and something to limit the current. The easiest way is to steal B+ from some other piece of tube equipment that has the right voltage, just connect the capacitor to be reformed through a large resistor, such as 47 or 100k, 5 watt. And leave it on for several hours while monitoring the voltage across that resistor, if the cap is usable it will die away to almost nothing.

[km6xz]

Modern electrolytic caps have their primary limitation with temperature, whereas the old ones made in the 1920-30s ( Mershon caps) had a short life due to evaporation. If you are restoring an old radio, prior to WWII this is a major concern and reforming the oxide layer is often not possible due to dry electrolyte. Just replace them, new styles are smaller for voltage and value so retaining the paper or metal can of the original, and fitting modern long life caps inside will preserve the collector value.

Modern electronics, 1950s and later, the evaporation rate was much lower so 20 years was possible if temperatures were not elevated and reverse bias was prevented. A cap that is operated in a room temperature environment will last decades, but 100C will shorten their live dramatically. Tube amps have elevated temperatures unless cooling is part of the design. The difference between 50 degrees C and 85C is about double the life. In switching power supplies in computers and new amplifiers the heat of caps becomes more of an issue again. Heat kills them but before dying completely their ESR increases a lot, making them poor choices to keep in the unit, even if the capacitance meter says they are OK, it does not measure ESR. The higher ESR, means higher heat dissipation of the cap, which further increases ESR, and further loss of water from the electrolyte. Those are the only caps I routinely replace in circuits after estimating the life heat history of the unit. If the cap relief plus or cross scoring of top starts to bulge, they might measure fine on a Cap meter but guaranteed that they have high ESR and no longer filter well.
Other than electrolytic, wholesale replacement of caps seldom does any good except cost the customer a lot of needless expense. Even electrolytic coupling caps or cathode bypass are often fine if not subjected to excess heat or reverse biasing. The low voltages present in the cathode circuit means the cap will last much longer than those run closer to the upper limit of voltage and temperature.

[rounder]

So NEW caps don't need formed or slowly broken in, just old ones?

Tnx, Zig

[pdf64]

Correct.