[Boatanchors] Chemicals to remove old stains on switch wafers

[JAMES HANLON]

Richard wrote:
 Do you mean the contacts or the wafers?  If the contacts I
would stick to Deoxit D-5. They may be silver plated brass in
which case you are seeing silver sulfide. A silver cleaner of the
sort sold for cleaning dinnerware will certainly take off any
oxidation and leave bright brass but takes off a lot of metal.
Not something I recommend.
    If you do clean them to where they are bright metal I suggest
coating them with a very thin layer of Vaseline or silicone grease.
     I would be much more concerned with how they work than how
they look.

On 7/6/2022 12:23 PM, Yongsurk Lee, HL1FB wrote:
> What would you use to remove old stains and oxidations on vintage selector
> switch brass contacts on wafers? I am restoring old TV-7 tube testers and
> want to make the switch wafers like new, bright and shining.

I would recommend NOT using silicone grease on or anywhere around electrical contacts that might spark when they are switched.  This comes from an old Bell Labs hand (moi) with hard experience with silicone oil around the relays on 400G Key Telephone Units.  The free silicone oil from a potted reed relay migrated across the circuit board and up the springs to the contacts of some open contact relays which were switching 24 volt, arcing circuits.  The silicone oil broke down under the heat of the arcs and formed non-conducting silicon cinders, thereby putting the Key Telephone Units out of business.  Silicone oil is very slippery stuff, which is why it is such a good lubricant.  One molecule of it will not stand on the top of another molecule if there is space for it to spread out, so it will keep going until it forms a thin film of silicone oil everywhere around its initial source.  Any place it goes, if it meets a low energy electric spark it will break down and form an insulating cinder.  (Very energetic sparks may blast the cinders away.)  It's possible if you introduce a source of silicone oil into a TV-7 tube tester that you could wind up fouling the contacts on a good many of the switches.

I'm not sure about Richard's suggestion of using Vaseline.  As I understand it, it is petroleum-based, so it probably would not be as bad as silicone grease.  The good effect it would have would be to keep oxygen away from the contact metal surfaces and thus retard oxidation.  But it might, over time, as its lighter components evaporate, simply gum up the contacts.  We had a situation at a Florida Air Force Base where a flood soaked a crossbar-switch type telephone office during a hurricane.  The folks who were working to recover the office sprayed all of the switches, which are open contact types, with WD-40.  Well the WD-40 did do its Water Displacement job initially and the office started to work again.  But several months later as the lighter constituents of the WD-40 evaporated, it left a gummy deposit on the switches which completely destroyed their operation.  They finally had to replace the entire office.  This might not happen as readily with rotary switches which have a good amount of "wipe" as they are moved to different positions.  But basically you are asking for trouble if you introduce something gummy into a switch contact.

As Richard says, be much more concerned about how the switches work than about how they look.  The conservative thing would be just to treat them with Deoxit to start with and then to repeat the Deoxit treatment in the future whenever they need it again.  That's what I do with the bandswitch on a National NC-173 receiver, and it's still running OK after its start in 1947.

Jim Hanlon, W8KGI