It is currently Fri Jun 05, 2020 6:44 pm


Cleaning wire key contacts

Building organ consoles for use with Hauptwerk, adding MIDI to existing consoles, obtaining parts, ...
  • Author
  • Message
Offline
User avatar

JohnNicholson

Member

  • Posts: 55
  • Joined: Mon Mar 23, 2009 6:03 pm
  • Location: North Wales (Bangor)

Cleaning wire key contacts

PostFri Mar 06, 2020 4:35 pm

I have six Compton style electric manual keyboards that have wire contacts swept by a copper T shaped wire attached to the end of each key, (a two manual office console, and a four manual main console). I am finding a lot of these are not striking cleanly. Has anyone got any advice on how best to clean or improve the life of these wire contacts?
John Nicholson
Offline
User avatar

engrssc

Member

  • Posts: 6447
  • Joined: Mon Aug 22, 2005 11:12 pm
  • Location: Roscoe, IL, USA

Re: Cleaning wire key contacts

Offline

larason2

Member

  • Posts: 126
  • Joined: Thu Feb 04, 2016 10:32 pm

Re: Cleaning wire key contacts

PostSun Mar 08, 2020 12:07 am

Along these lines, once the contacts have been cleaned, I wonder if a product like this would be recommended to protect them from re-oxidizing...

https://canada.newark.com/electrolube/s ... p/10WX6357

Anyone have any experience with this?
Offline

rayjcar

Member

  • Posts: 56
  • Joined: Mon Mar 17, 2014 10:56 am
  • Location: Toronto, Canada

Re: Cleaning wire key contacts

PostSun Mar 08, 2020 7:15 am

I would definitely stay away from the grease. In reading the .pdf data sheet, near the bottom it says:

"Thus the grease is preferable in industrial applications where heavy arcing is common. For example: battery terminals, knife switches, rheostats etc".

Keyboard contacts in midified organs have only a fraction of a milliampere flowing. The encoder cards typically have a 20k ohm series resistor in the input circuit. There is no arcing whatsoever. It is true that pipe organs with electropneumatic switches (such as used by Wurlitzer) could have arcing at the keyboard, not only because of the amount of current pulled by the electromagnet, but also because of the back emf caused by collapse of the magnetic field of the electromagnet when the contact was released.
Offline

Cooky

Member

  • Posts: 128
  • Joined: Thu Jan 01, 2009 6:29 am
  • Location: Melbourne, Australia

Re: Cleaning wire key contacts

PostSun Mar 08, 2020 11:55 pm

I have an unmidified 2 manual Compton CS357 Electrone (1960).
The voltage across the contacts is huge - it will give you a serious bite!!
As Rayjcar suggests, this system keeps the contacts clean via voltage arcing.
I expect that Compton pipe organs used the same contact system and voltage - all using classic ivory clad, wood core, long pivot keyboards.
Midifying these keyboards would almost certainly require an encoder that will work with a high voltage in order to maintain reliable contacts. Had the contacts been gold plated it would be a different story.
Offline

ppytprs

Member

  • Posts: 156
  • Joined: Wed Sep 03, 2014 5:07 pm

Re: Cleaning wire key contacts

PostTue Mar 10, 2020 7:53 am

I use 1200 grit sandpaper to clean these. They tend not to be reliable though once they're so old. As others have said, there's no power in modern electronics to keep them clean. Better to replace with new, or a magnetic system.

Why have you got 6?!
Offline

rayjcar

Member

  • Posts: 56
  • Joined: Mon Mar 17, 2014 10:56 am
  • Location: Toronto, Canada

Re: Cleaning wire key contacts

PostTue Mar 10, 2020 10:15 am

One approach would be to wire a 100 ohm 2 watt resistor across the output of the key contact to ground (assuming a positive keying convention). In effect that resistor would be in parallel with the input to the midi encoder. The 100 ohm load is roughly equivalent to the resistance of a single Wurlitzer magnet.

By so doing, the keyboard contact will be pulling 120 milliamps, which should be sufficient to get around a scratchy contact.
The encoder will still see the 12 volt keying voltage, and the momentary dissipation in the resistor will be 1.4 watts. Most midi encoders have contact debouncing, which should resolve and contact bounce issues.

Ray
Offline

GrahamH

Member

  • Posts: 562
  • Joined: Tue Sep 09, 2008 7:39 am
  • Location: Near Manchester, England

Re: Cleaning wire key contacts

PostTue Mar 10, 2020 3:32 pm

I'm with "ppytprs" - up to a point, at any rate...
Better to replace with new, or a magnetic system.


Over the years I have midi-fied a number of ex-Compton wood-core keyboards.
The first pair that I acquired came without the original key contacts anyway, so I fitted reed switches and magnets.
Some time later I acquired a pair that still had their original contacts attached – albeit damaged or incomplete. One look at these “cat’s cradle” arrangements was enough to convince me that only a masochist would attempt to restore them, so I removed them and fitted reed switches!
At that time I was a firm advocate of reed switches and magnets, but more recently I did some experiments with photo-interrupters (opto-switches) and did a proof-of-concept exercise by fitting them to an ex-Compton keyboard.
In my opinion, this is definitely the way to go. The photo-interrupters are so much easier to adjust than reed switches and magnets, and there are none of the hysteresis or cross-talk issues that you have to contend with if you employ magnets. Also, they are cheaper!

Bite the bullet! - You won't regret it!

Graham

Return to DIY organ consoles / MIDI

Who is online

Users browsing this forum: No registered users and 1 guest