[R-390] thanks

[2002tii]

Roy wrote:

>The 60 volts will appear on an ungrounded chassis if the line filter
>is working correctly.  It's not clear to me how the line filter can
>cause a mechanical audible hum (that is, not heard in the audio
>output, but rather coming from the radio itself.)
>
>Can someone explain this to me?  (I certainly can explain the 60 volts.)

That was my thought, a well.  There are two inductors inside the line 
filter (the filter consists of two independent C-L-C pi filters, one 
on each supply leg), so it is at least theoretically possible that 
one or both could be generating mechanical hum -- but this is not, to 
my knowledge, a common problem with the stock line filters.  Thus, it 
seems unlikely (but not impossible) that this was a source of mechanical hum.

As Roy notes, the 60 volts on the (ungrounded) chassis is NOT an 
indication that the line filter is faulty -- it is generated by the 
voltage divider formed by the capacitors in the filter, the mid-point 
of which is connected to the chassis.  Half of the nominally 120 volt 
mains supply is 60 volts, so that is where the chassis sits if the 
radio is not grounded.  When you ground the radio, the 60 volts 
disappears, replaced by a significant current flowing in the ground 
wire (which will trip a GFI, as previously discussed).

Best regards,

Don