Ultrasonic Cleaning of Old Radio Parts

by Robert Lozier - Copyright 1997/2008

Properly cleaning the small hardware in the old equipment we get is probably the least enjoyable part of the hobby of collecting and preserving old radios.  Even after you thoroughly clean some parts, there still remains some visible oxidation or other deposits that you just cannot get at even with a very fine brush and plenty of  "elbow grease".  If the part happens to be a nickel plated thumbscrew, you are likely to remove much of the plating on the high spots before you ever clean out the crevices in the knurling.   Such problems can be eliminated to a large degree by using an ultrasonic cleaner to do the job.  It is easier, faster and the end result is better! 

There are a number of small cleaners on the market, I have found the best size for use in our hobby is one with a tank that is about 9" long, 5" wide and 4" deep.  This will hold about 1/2 gallon of water.  That may not sound very large, but it is big enough to drop in the frame of a Philco 90 tuning condenser and that is just about the largest thing I have ever needed to clean.

Cleaners of this size will cost $325 to $450 when equipped with a timer and tank heater.  That sounds like a lot of money but think of it as an investment that will allow you to do a better job of cleaning and preservation of your collection which may be valued at 10, 100 or 1,000 times that much money.  A properly cared for cleaner will last 10 years or more....

There is quite a lot of variation in the cleaning power of various brands of cleaners and the highest priced cleaners are not always the most powerful or made of the most durable materials.  I would suggest that you consider the Electrowave brand of cleaners.  The energy density is about the highest in the industry and the cases are all stainless steel. 

Electrowave Inc., Call (903) 487-0896 or http://www.electrowavecorp.com/
Note: Unless you can buy this under a business purchase order, you might have to ask them for a retailer for their product.  Several years ago I was able to purchase this brand through a mail order clock supply house in Oregon using my Master Card but they are apparently no longer in business.

An ultrasonic cleaner uses cavitation to clean a surface.  In the cleaner there is a high frequency power oscillator that excites one or more piezoelectric elements bonded to the walls of the cleaning tank.   When the parts to be cleaned are put into the tank, microscopic air bubbles become trapped in and around the dirt and oxidation.  The high frequency energy (about 41 kHz.) cause these small bubbles to expand and collapse in such a way that local pressures in the bubbles reach thousands of pounds per square inch.  The violent collapse of the bubbles bring the cleaning agent into near perfect contact with the material to be removed.  The speed and completeness of cleaning can be  dramatic if the proper cleaning agents and the proper cleaning sequence is performed.

Poor cleaning action can almost always be traced to the use of the wrong cleaning agent and not to the ultrasonic cleaner.  Agents that work well with "elbow grease" often prove useless in such a cleaner.  The most important thing to remember is that any agent must have the lowest possible surface tension.  Most household cleaners have in them chemicals that are designed to hold dirt in suspension until it can be rinsed away.  These chemicals tend to raise the surface tension of the cleaner and thus reduce the wetting capability of the cleaner.  On a microscopic scale, this means that the cleaning agent never actually comes into direct contact with some of the dirt.  The other thing to remember is that you will not be able to clean off water soluble dirt very well if the parts have a film of oils, waxes and resins on them.   And… you cannot remove oxidation if it is covered by dirt and oils.  It is therefore necessary to clean the parts in several types of cleaning agents to do a complete job in the least amount of time.

A typical cleaning procedure would go like this:

The first cleaning step would be to run the parts thru a degreaser if you suspect that the part has old oil, wax, varnish or shellac on it. With any solvents, observe the need for proper ventilation, handling and storage.  Force dry the parts with a warm air gun such as the Makita Model HG1100 (An excellent design that I can highly recommended because of its fully adjustable thermostat control).  It works great for flow soldering Stay Brite low temperature solder into corrosion pits on parts you are preparing for plating.   And… It costs only about $75… An expense you will never regret.

With the oils removed you can now remove the water soluble dirt.  Use a little dish washing detergent and a tablespoon of fabric softener for this job (The fabric softener reduces the surface tension.)  If you think the parts can withstand it; you can use a cleaner like Castrol Super Clean.   Force dry the parts with a warm air gun.   If you think your detergent leaves any kind of film on the parts, give them another quick cleaning in clean degreaser.  Always force dry the parts.

You now have really clean parts and are now ready to remove any non-ferrous oxidation  on the parts.  This is done with a weak solution of a dry acid such as sodium bisulfate.  This is the acid used to reduce the pH level in swimming pools and spas.   It is very cheap, available at any pool store (even Wal-Mart) and easy to use.  Just dissolve one to three teaspoons of the acid in a pint of warm water.  At this strength, there is no problem if you get it on your hands and it will not react very much on your parts until the ultrasonic cleaner is turned on. 

After cleaning the parts in the acid, be sure to run the parts through two changes of clean water.  I would recommend the use of distilled water for the last change of water.           (Distilled water is cheap and my accelerated environmental tests have proven that it can make a difference.)  Force dry the parts as fast as you can!!!

All the parts you clean MUST be given a coat of clear lacquer to retard future oxidation.  There are a number of quick dry spray lacquers that do not produce a really glossy finish.
One of my favorites is Eastwood’s Diamond Clear Satin Aerosol.  For brass work, I keep a can of heavy brushing lacquer that I can stain with aniline wood dye to give the brass that antique look.