[HAM] B-3 hum & percusson switches

[Geoff Williamson]

I recently visited a B-3 with a couple of issues, there was a mild  
50Hz hum in the organ (I think it was 50Hz, same pitch as G1 on the  
16' anyhow), percussion would not decay fully and the organ needed a  
428 trem kit in place of the make-shift arrangement that 'borrowed' DC  
from the percussion circuit and sent that on pin 5 down to a make- 
shift relay arrangement mounted on top of the 122 amp.  After fixing  
the percussion decay and correcting the switching circuits in the  
organ and Leslie I found the organ still had the hum (I had hoped that  
the fart-arsing around with the switching was the cause of the  
hum...but no...

Sadly I had to leave this job before fixing the hum - so here's my  
question - the hum is louder with percussion volume on 'Normal' and  
decay on 'Fast', regardless of the position of the other percussion  
switches (eg. with percussion on or off it makes no difference).  The  
hum is gone with any playing key depressed.  No other variables affect  
the loudness of the hum apart from the position of the expression  
pedal and the Leslie input volume pot.  Any suggestions where to look?

It will probably be a little while until I get back to this organ as  
the hum is only an issue for recording, but any suggestions will be  
very much appreciated if this issue sounds familiar to you...

Geoff