TS-520S transmit hum

[ko4kl]

Stations receiving my SSB signal detect hum. Removing the microphone from the radio did not fix it. I went to the CW mode and transmitted CW and no hum was heard by the receiving station. Since the hum is not there on CW I don't suspect the 800 volt (PA) or 300 volt (driver) supply filter capacitors. That leaves the 14 volt supply filter capacitors (2200 @ 16v) that supply the solid state devices. But if they are the cause of the hum why do I not hear hum in my receive audio since they use the same 14 volt power as the transmit audio? Any help pinning this down would be appreciated.

 

[Sonwatcher]

From an old post on another forum:

I have hum on my SSB signal. Several stations have complained about it, should I send my rig to you?
Before you send it off for repair, a simple check might solve your problem. Kenwood used separate grounds on the MIC connector for the PTT switch, and the microphone signal and ground leads. If your microphone is mis-wired, and I have seen a number that are, you will get hum on your signal. Kenwood stresses in their owner's manuals, "KEEP THE GROUNDS SEPARATE" but some people have to learn the hard way. If pins 3 and 4 on your microphone connector (on the microphone cord itself) are connected, you will have hum.

K4EAA FAQ

 

[Randall]

your receiver section does not use as much current as your transmitter, try a higher wattage power supply, or if it worked fine before check the large filter caps in your supply if it is a linear supply.