[Hallicrafters] Help with restoring the shine to tuning capacitors

[GARDGORE at aol.com]

Let me begin by saying it does take some knowledge of materials and cleaning 
agents and their effects along with a lot of previous experience to properly 
clean a communications receiver and have it turn out looking like really 
professional looking work. Often someone just starting out cleaning radio equipment 
will cause a lot of damage in the course of the job without really realizing 
what is happening due to not protecting what needs to be protected and improper 
choice of cleaning agents or combinations of agents. When selecting cleaning 
agents for cleaning your tuning caps you should keep in mind they are an 
assembly of several different types of materials. The plates are usually aluminum, 
the frame is either tin, cadmium, or zinc plated steel. The shafts are either 
brass, nickel plated brass, or cadmium plated steel, the wipers are either 
copper or brass and there are either ceramic or phenolic insulators. It is 
important to rinse thoroughly because cleaning agents can easily be left behind and 
lodged between surfaces that are clamped together in an assembly to form 
corrosive salts which will begin to degrade your parts over time afterwards. Each 
material mentioned requires a different cleaning agent for best results. In the 
case of the aluminum plates it is not possible to restore them to their 
original luster if they have become seriously discolored. Most folks resort to 
polishing to improve the appearance of aluminum but this results in a part that 
does not look original (though it might look better). The cadmium plated steel 
can be brightened by washing with a solution of sodium bisulfate and warm water 
(mild acid- wear rubber gloves) followed by a second washing of ammonia and 
water. Probably the most effective cleaning agent for discolored aluminum is a 
50-50 mix of ammonia and 409 followed with a thorough rinsing and blow dry to 
get it dry again as soon as possible.

Regards, 
Greg Gore; WA1KBQ