[HAM] Motorboating vibrato

[Dave Bishop]

Try replacing the 6AU6 tube on the preamp that is farthest to the right (or 
swap the 6AU6 tubes).  Check the screen and plate voltage on tube V2.

Check for a disconnected wire (black) from the scanner to the drawbar base 
and at all the solder joints on the line box.  A missing line will make the 
vibrato sound choppy.

Does the motorboating change as you flip through the vibrato/chorus knob 
positions?  If so, check for a short at the shield on that rotory switch.

If you do have motorboating, dust or dentrites probably are on the pole 
pieces or locating pins in the scanner, shorting to the stators.  That's not 
to say there aren't shorts in the vibrato switches, just that they aren't 
the first place I'd look for motorboating.

To flash the vibrato tie three 9 V batteries in series and ground the - side 
to the pre-amp chassis.  Using a wire from the + side of the array, and with 
the organ unplugged, touch each of the screw wire terminals on the top of 
the vibrato scanner. Touch the joint of each of the seven wires on the upper 
left soldered above the scanner, with the switches placed in all positions.


Regards,

Dave Bishop