[HAM] C3 rumbling

[Dave Bishop]

You could check the DC voltage on your pre-amp outputs at G and G terminals. 
At full volume with all drawbars out and six notes pressed on each manual, 
you should see about 3 to 3.5 volts P-P between a G terminal and chassis 
ground.

If yours is low, you can open the air capacitor shielding, press the 
expression pedal down, loosen the bolt holding the pedal rod to the arm and 
hand adjust the travel of the air cap blades until you get highest 
voltage/sound level.  Then tighten the arm back up.  You may also have 
12BH7A  tubes V3 and V4 that need to be replaced, or weak B+ voltage because 
the electrolytic caps are going bad or the associated resistors have 
drifted.

 Its a good idea to spray a small amount of De-Oxit into the tube sockets to 
remove corrosion on the pins.  Also spray all the connectors between the 
organ and the Leslie, since corrosion can cause a weak signal.  In my 
experience a 145's smaller cabinet means lower volume than a 147, but my 
favorite method of competing with the guitars and drums by far is mic-ing 
the Leslies into a bass amp or FOH.

Regards,

Dave Bishop