Basic keyboard contact & feed wiring

[ChristopherS]

I’m working with a salvaged keyboard which will be used to test wind-chests of 1875 Henry Erben organ (electrified in 1920s) which had its console removed 25 years ago. The salvaged keyboard has contacts only, at end of each key. So I ‘think’ this is how it should be wired:

1. a single common 12Vdc Positive comes from rectifier to a single common under the contacts.
2. The contact of each key then goes to each chest magnet, via the spreader board.
3. The negative returns to the rectifier via the common Negative at the wind-chest.
4. So for the keyboard itself I only need a common Positive feed going in, as well as each Positive wire coming from each key contact, going out to the spreader board.

>>Do I have this right??<< Thanks for your comments. BTW last week I tested the magnets of the Swell wind-chest by connecting the Positive of a 12Vdc “wallwort” transformer to each Swell note wire at the spreader board (via alligator clip), and the transformer Negative to the common Negative coming off the wind-chest--and I’m happy to report that all the Swell magnets work and all the pallets on the 1875 Swell slider chest work! The Swell has some extraordinarily beautiful stops, including an 8’ Oboe and 8’ celeste: which sounded for the first time in 25 years. The week before I finished installing a new motor starter for the 100 year-old blower motor (rebuilt c. 30 years ago). I turned on the motor, it started up perfectly and the organ had wind for the first time in 25 years with no significant wind leaks. (Reservoirs look like they were releathered not long before a previous pastor halted work and sold console.) So major progress!

[Larrytow]

Yes, you have the correct understanding of how to wire the keyboard contacts. Key contacts on an electric action ( EP, EM, Etc. ) pipe organ are nothing but momentary, normally off, switches anyhow. After you have all the keys wired to the chest, you should use a larger amp capacity 12 volt supply though. For testing one magnet at a time the wall wart can work, but if you start playing chords on the keyboard it will likely fail quickly.

[ChristopherS]

Larrytow Thanks, Larry. The wall wort is just a temporary testing device. The organ actually has a rectifier, but we are not using that for now do to possibility of shorts in the disconnected console cable, which could be hazardous.

[Coenraads]

You are wise to be wary of the organ rectifier. I'm working with a 70 A supply while installing a legacy switching system on a 4 manual Casavant at the moment. I don't even wear my ring wedding ring while working on this brute, well aware that a short circuit will instantly heat the ring to red hot.
Here is how I make testing safe. I connect a 5 ohm, 10 W wire wound resistor in series with the rectifier output going to the organ or, in your case, the keyboard. This limits the current to a relatively safe 3 A or so, low enough not to interfere with testing but enough to keep things from melting.
I also wired in an old (analog) voltmeter (after the resistor) so that I can monitor the voltage at ,all times while I'm testing. If the voltage suddenly drops, I know I have a short that needs to be located and corrected. Yes, you could use a fuse, but I find it a nuisance to keep replacing them.