Need SB401 Elmer Help!!!

[Dan Pividal N4VET]

Have an SB401 that has developed a hum when the mike is keyed down with no
modulation.
Mike can be removed and pins on radio shorted and hum is still heard on my
Kenwood receiver with its antenna disconnected.
I have changed out the 6ea8 tube on the audio preamp board and no change.
I have checked all of the mike connections in the radio. All are good.
My book shows C101 and 102 limits low and high frequency response.
I do not think this is the problem.
However, C102 also passes rf to ground that is picked up by mike.
Could this be the culprit?
I have no place that will work on this rig in Tampa so I have to fix on my
own.
Any help would be great.
I know with all the Heath people out on the reflector somebody has had this
problem before. Please share your fix.
Thanks,
Dan N4VET

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