First I got the upper manual (ie. keyboard assembly with internal contact switches) out of the organ and stood it up on its left hand end (next time I'll definitely unsolder all the wires and put the manual on a bench...d'oh!). Then I took the metal covers off from the top back and underside to get at the manual wiring loom...
Now check this stuff out....I nearly stopped before I even started when I saw how many little wires there were inside one of these little Hammond organ manuals....it looks like the web of a spider suffering obsessive-compulsive disorder!
You'll see that I have marked the frequency lugs with numbers, 80-91 being the important frequencies here...I added extra contact wires to so that these highest frequencies became available on the last 3 drawbars (as on a console model). Luckily I had a chart to copy, along with instructions kindly sent by Patrick Bianchi (thanks Pat!). The contacts at the end of these wires look like this:
The busbar on the right has a fine paladium wire on the top (they stand edge up) and the short section of paladium wire on the end of the copper (?) contact is pushed down onto the wire on the busbar when you press a key on the organ. Clever fellow Mr. Hammond - he used paladium to make sure these things last a long, long time without corroding (decades and decades....)
Working out which of the 9 busbars sent which frequencies where was the tricky bit - they are not in the same order sequentially as the drawbars that receive the signal from them....cunning I reckon....almost buggered up my project....see how there are 9 busbars piled in there...I had to replace 3 shorties with 3 full-length busbars so the extra contacts had some place to make contact with...errr....
To get the contact in or out, I had to pull out a small bakelite (phenolic type material) locking piece, and squeeze the 'legs' of the contact close together so it can slip through the gaps....see below one of the contacts going in with its 'tail' of resistance wire dangling in the breeze (I heard that these contacts with their little tails are known in some circles as the spermatazoa of the organ...) Before I forget....I must thank Mike Fulk at this point for encouraging me to tackle the project in the first place...and thanks also to Steve Leigh for the extra busbars and good advice.
Finally after sorting each lot of extra resistance wires and soldering them to the appropriate frequency lugs, or so I thought, then the only challenge left was how to put the manual back together. After a while I found a place for everthing and fired up the organ...with only one frequency out of place, I was able to resolder the wire without much dismantling and away it went, in all of its full harmonic glory!!!
You can do the 'add foldback' modification yourself with Pat Bianchi's instructions - just don't forget you'll need to unplug the organ and make sure you don't go anywhere near the high voltage areas of the amp or pre-amp before the filter caps have fully discharged (if in doubt get a qualified technician to do this stuff, electronic equpment can be lethal, etc...) Here's the instructions:
Pat Bianchi's Foldback Instructions
now for the sicker spinet fans amongst you...
on to Lower Manual Bass Mod back to Geoff's Hammond Page