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Most vintage parts aren’t very clean when you find them. Years of dust, dirt, and sometimes just plain grime have built up. It is highly desirable to clean the parts before using them. With some items this is easy; with others, not so much. One of the toughest items to clean is variable condensers. The goal is to clean and restore the parts to as near original condition as possible, without doing any damage in the process. Many vintage condensers contain insulating materials such as hard rubber, which could be easily damaged during cleaning. The plating on some metal parts can be quite thin and easily removed by any abrasive. Some variable condensers can be completely disassembled so that each and every plate, spacer, etc. can be cleaned. Others, like the Cardwell Type B which I’m cleaning today cannot. The stator plates of the Type B are swedged ito aluminum blocks and cannot be separated. That makes it challenging to clean them fully. So how does one clean such a thing? I had heard of various methods, but either could not find details or did not have the apparatus needed (such as an automatic dishwasher). So I set out on my own to find a method I could use. I did some research on methods for cleaning delicate metals, then experimented on non-precious (not antique) parts until I came up with a method I was comfortable with. The method to be described is probably not the best way of restoring these condensers, but it works well enough for my tastes. It is possible to damage the parts with this process if care is not taken.
The first step in the restoration process is to disassemble the variable condenser, either fully or partially depending on its design and one’s preferences. With the Cardwell Type B, I leave the rotor assembly intact. The stator assembly, as mentioned previously, cannot be taken apart. I also don’t remove the shaft bushing from the front end plate or the bearing/tension adjustment from the rear end plate. Most variable condensers have a ball bearing at the rear of the shaft. It is very important to watch for this, as it could easily get lost. It may or may not roll out on its own, as thee grease might hold it in place when the unit is disassembled. Some variable condensers may have several ball bearings in a race at the front or rear. Be sure to note how the parts were assembled.
After disassembling the condenser, it is very important to remove all grease before doing anything else. There will be grease on any ball bearings, bearing races, shaft bushings, etc. My method of removal is 99% rubbing alcohol and cotton swabs. Changing the swab frequently, I continue wiping until I see no evidence of further grease being removed. In other words until the swab remains perfectly white after repeatedly wiping the greased areas. Failure to remove all grease at this point will almost certainly result in unacceptable results later in the restoration process.
The next step is to pre-treat the parts before boiling. Using a paste made of cream of tartar and water and a soft cloth, I rub/buff all the larger metal parts; end plates, round spacers, the outermost rotor and stator plates, edges of all plates, etc. Areas with accumulated grime may require additional rubbing to get it off. After buffing each part, rinse it with water and inspect it. If it doesn’t look reasonably clean or has spots that still appear dirty, it needs further work. I do not clean the hard rubber strips this way. More on those later. I place the smaller hardware items – nuts, screws, washers, ball bearing(s) into a jar with a tight fitting lid. I put about1 tablespoon cream of tarter and one ounce of white vinegar in the jar, put the lid on, and shake moderately for a several seconds. I then let it sit a few minutes and shake again. It is not wise to shake too hard or too long, as plated parts may be damaged easily. I then remove one or two parts, rinse them, and inspect. If they don’t seem to be reasonably clean, I then add 2 tablespoons of baking soda to the jar, and enough water to get a liquid emulsion. I then shake for 30 seconds or so, no longer. The small parts should them be removed and rinsed thoroughly. I find a plastic strainer very handy for this step.
Now it is time to boil the condenser. All parts except the hard rubber strips are placed in a stainless steel sauce pan. I add enough water so that all parts are completely covered, then add about 1/4 cup of white vinegar. After this is brought to a boil, I reduce heat, cover, and simmer about 45 minutes, gently rearranging the parts once or twice. At this point the parts should look very clean and uniformly shiny. All parts should be removed from the cooking solution and thoroughly rinsed with clean water. Distilled water is preferred but any water is better than not rinsing. I rinse the smaller parts in a plastic strainer. At this point I only handle the clean parts with wood or plastic implements or while wearing vinyl gloves. I do not want any skin oils getting on the parts. It may be just paranoia, but I don’t want to risk the presence of any foreign contamination causing the parts to dull more quickly in the future.
While the metal parts are cooking is a good time to clean the hard rubber parts. I use 99% rubbing alcohol and a soft cloth to clean those. It is best to use a light colored cloth, or strong paper towel, so as to be able to see how much dirt is coming off the parts. I continue cleaning until I’m not seeing any more dirt accumulating on a clean section of the cloth. I then wipe them dry with a clean, dry cloth. That is all there is to cleaning the hard rubber parts.
After shaking off as much water as possible from the metal parts (post rinsing), I arrange the parts on a glass baking dish, then bake in an oven at 200 degrees F for about 20 minutes or until completely dry. Gently moving the parts around every few minutes will help. It is not wise to bake any longer than necessary to get the parts dry. Convection baking is better if available. Plated parts sometimes look a little off color after drying, but I have found (so far) buffing with a soft, dry cloth brings back the proper color. I’m not sure what is causing this discoloration.
Before reassembly, the shaft bearing(s), ball bearing(s) and any associated friction areas should be given a small amount of lubricant. Many people use light machine oil. I’m sure that works just fine, but it seems apparent to me the original lubricant was grease of some sort. I like to use a very small amount of moly high temperature grease, mainly becuse that’s what I have available. I apply it using a toothpick.
All that remains now is to reassemble the condenser. I like to start by laying out the parts in a convenient manner before starting this, but it’s not important as long as one remembers which items went where, and how. I wear vinyl gloves for the entire reassemblyprocess, to avoid contamination as noted previously. Then end result should be condenser which looks close to original condition.
A few additional words on reassembly may be in order. These Cardwells are fairly user friendly to assemble, but if the plates don’t seem to mesh quite right after it is put together, the hard rubber strips may need to be adjusted slightly. Slightly loosen the screws holding the hard rubber strips to the end plates, and you should find the strips can be moved fore and aft slightly. If this doesn’t correct any misalignment, it is possible the left and right insulator strips were reversed during assembly. Swap them and check again.
Some other types of variable condensers are less friendly to adjust correctly after putting them back together. I once spent half a day fooling with a National Type DX condenser after I had cleaned it. The plates just didn’t want to maintain spacing correctly at all settings. It was a matter of adjusting the hard rubber insulating strips and the nuts that control the position of the stator plates on the stator plate mounting rods. I had completely disassembled the Type DX for cleaning… every nut, every plate, every spacer. That is a lot of small parts!