Vintage Synth Repair

On your A-143 and B3’s ect.

The 16’ drawbar (Sub fundamental) is at -14db compared to the next octave up which is at -3.5db. Therefore it will not have the same volume as the next octave up. This is partially accomplished with resistance wires from the key contacts back to the terminal strip on the keyboard where the tone wheel outputs are connected.

The key contacts make contact with the buss-bars which are wired to the preset panel (on the right side) in turn is wired to the matching transformer. The matching transformer sends the audio to the control panel (vibrato on/of switches) than to the pre-amp at the (A) input (vibrato off) or the (B) input (vibrato on).

FYI

The sub fundamentals first octave is also a repeat of the second octave. In the Hammond world it is called fold-back. (C1 & C2 are the same note with the 16” drawbar).

1) Make sure this happens with vibrato on and off.

2) If all your screws are tight on the preset panel,

3) the only place for this fault to occur is at the key contact and buss-bar.

Unless your keyboard is prone to gooey foam corrosion.

Around 1964 Hammond switched from using felt to assist in sealing the keyboards from contaminants to foam rubber. On some organs (dependent on location) this foam rubber turned into corrosive goo and is destroying the resistance wires mentioned above. If you do not know your organ’s build year, get the serial number of the organ, you can go to:

http://www.tonewheelgeneral.com/agelist/agelist.php

And look up your build year.

There are also ways to check to find if you do have foam rubber in you organ. Another topic!

Mike