"Kevin Seal"


The 100uF 6.3V capacitor C2 on the input I.C. is the usual culprit for
hum.


** That ( tantalum) cap has nothing to do with any hum problem.

http://www.geocities.com/quad_esl63/...c/power405.jpg

It is a response setting cap for the DC offset servo.


But as others have said, I would change all the electrolytics on the PCB.


** Which will have no effect on the OP hum issue.

His 405s have been modified in a way that is highly prone to creating hum.




........ Phil