[R-390] R390: 60 Hz on Audio

[Flowertime01 at wmconnect.com]

Jon,

It is clean and good on the 16KHz filter. 
V502 confirms the problem lies prior to the plate output of V502.

Its back to the band switch and filter sections.

It is not V501 as it does not appear in the 16KHz switch position.

A wire for 2, 4, 8 is laying to close to a 60Hz source.

S503 rear is not giving you the ground you expect on the 2, 4, 8 filter 
when you are selecting those filters. The switch section is not grounding the 
other filter sections as expected. The other filters are floating, picking up 
AC and passing it down the line.

At 16KHz, either the switch section is working. Or the other 3 filters are 
not getting enough 60Hz coupled into them to present the problem.

I think the 16KHz filter is picking up the 60 Hz and passing it down the 
wire when you are using 2,4,8. At 16 you change the switch setup and thus do 
not see any 60 Hz.

Keep testing.

Roger AI4NI