On my linear astron supply I tightened the bolts holding the transformer plates and also replaced the rivets that were holding the transformer to the case with nyloc nuts and bolts. My supply is now silent.
On Apr 19, 2019, at 7:55 PM, Jim - N4ST <firstname.lastname@example.org> wrote:
So, I noticed that my +25-year-old Astron 35M had developed a louder hum in the last few months.
Hum was worse on receive than FT8 50-watt transmit, which seemed peculiar.
Then I noticed this hum issue was gone if I turned off my portable electric heater.
Thinking I was hearing things, I put my fingers on the Astron case and verified by touch the above observations.
Moved the electric heater power cord to a different outlet/breaker than the Astron and hum issue was gone.
OK, geniuses…any theories?
Jim – N4ST