Had Descending Moonshine Dervishes, Terry Riley's live recording from November 1975, on the stereo this morning and we all just tripped out the entire rest of the day. How he managed to retune the Yamaha YC 45D combo organ to just intonation is anyone's guess. Aha, of course, not true, as these days everything is on the internet: "Yamaha YC-25D/YC-45D:
Remove the two screws securing the top These are underneath the organ, one on either side. The two closest to the back of the organ release the top. Lift the top up and find the oscillator board. If it's a transistor oscillator model, it will have 12 tuning coils on it. In the YC-20, it's mounted on the control board
On the YC-25D and YC-45D, it's in the card cage, the board closest to the pedal compartment. Remove the two screws securing the board. If it doesn't lift right out, but gets caught against the back of the cabinet, you may have to remove the two large screws securing the card cage, and nudge that end of the whole cage forward slightly, so the oscillator board will clear the back of cabinet. Be very careful of the wires. There are no dangerous voltages in this area, but you don't want to accidentally break one. You may also have to bend back the wire-tie securing the wire bundle to the front of the card, so that bundle can drop down the side of the card as you lift it out of the cage.
The oscillator coils are arranged as follows:
top of card, facing the coils.
| _ | _ | _
G D A E B F#
_ | _ | _ |
C# G# D# A# F C
If you're using a metal hex key, the pitch of the oscillator will drop about 5 cents with the key fully inserted into the coil, so tune it 5 cents flat, and it should be almost dead on when you remove the key
You'll need a 7/64" Allen wrench"
So there you have it folks. How Terry Riley tuned his Yamaha YC-45D.