I'm restoring a Howard model 318 Console. One of the electrolytic capacitors is a 8uf / 475 V (WET) aluminum can, which is spewing out of the top. So I need to replace the whole can. I'm thinking of stuffing another can that I have lying around that is in good shape. I have not found any mention of wet caps as replacements so I'm assuming a modern day electrolytic will do here. I'm planning on grounding the cap to one of the twist tabs going thru the chassis on the donor can.

I guess my main questions are...
1: Why did they even need "wet" caps to begin with?
2: Can I replace this wet cap with a modern day "dry" cap?

NA schematic for the 318 here...
http://www.nostalgiaair.org/Resources/259/M0009259.htm

Thanks in advance for any help.

Ron in RI

A modern electrolytic cap is fine there. I'm guessing all electrolytics are wet to some degree. We need a pro to answer this..

Here we go from wikipedia...


An electrolytic capacitor is a type of capacitor that uses an electrolyte (an ionic conducting liquid) as one of its plates to achieve a larger capacitance per unit volume than other types, but with performance disadvantages. All capacitors conduct alternating current (AC) and block direct current (DC) and can be used, amongst other applications, to couple circuit blocks allowing AC signals to be transferred while blocking DC power, to store energy, and to filter signals according to their frequency. The large capacitance of electrolytic capacitors makes them particularly suitable for passing or bypassing low-frequency signals and storing large amounts of energy. They are widely used in power supplies and for decoupling unwanted AC components from DC power connections.

At one time even rectifiers were wet. Technology improves and things
change. Those wet electrolytics were cutting edge when they were
introduced. You could replace them with a modern mylar cap, if you
have the room and could afford the cost Otherwise, a modern
electrolytic will work fine.

Pete

Since the original was rated at 475V, you might hang a meter there and verify that the voltage doesn't go too high during warmup. Wet electrolytics were more tolerant of overvoltage since they could absorb quite a lot of heat momentarily.

The so-called "dry" electrolytics are no dryer than a "dry-cell" battery. They are moist inside, and the seals keep the electrolyte from drying out. Without the electrolyte, you don't have a capacitor. They were introduced in the early 1930s, and really were cutting-edge technology for their time; they made the AC-DC midget radio possible. Wet electrolytics were used in AC-operated radios and amplifiers, where voltages were higher; they were still being used by Philco in 1939-40. Right about that time, Mallory introduced their "FP" type dry electrolytic capacitor, which eventually became the standard.

The lack of a good seal in the cardboard tube and box type of capacitor explains their high failure rate.

Regardless, put your goggles on before you fire up an old set which you have foolishly not yet recapped. Old caps can fail really violently, wet, dry, or whatever. Please Don't ask.

May have to pull your cat off the ceiling.....

Hi,

See volume 7 of 1948 NRI radio course. There all some good reading

http://www.km5z.us/NRI_Radio_Course.php

Vin

That NRI course, along with the smaller grey-covered "servicing methods" booklets, is the very one which I studied about 50 years ago! It's still good reading today.