[HAM] C3 Rumbling

[Dave Bishop]

If its intermittent its probably not in the cables.  I would first identify 
whether the rumble arises from the C3's pre-amp or the 147's power amp.  To 
do this I would attach a headphone set to the pre-amp with the Leslie 
disconnected.  You'd want to get a female 1/4 inch jack and wire the ring 
lug to a screw on the pre-amp chassis and solder the tip lug to one of the 
two G terminals.  Plug in a headset and you should get a weak sound out of 
one earpiece.  If you still get the same pattern of rumbling, it will be 
caused in the pre-amp.  If not, look to the Leslie.  The typical cause is 
failing electrolytic caps, which are those metal cylindrical cans on the two 
amps, and they can be replaced by a non-tech.  The next culprit on my list 
would be coupling caps and a plate resistor that is overheated.  Post back 
when you determine which amp is the troublemaker and the list can make more 
specific suggestions.

Regards,

Dave Bishop