Capacitors 4 and 5 are not normally in consumer units. Assume for this point of discussion that they are not in the unit and that these capacitors need to be installed. This is the major cause of rf feedback. Rf feedback is the signal from the station finding its way into the unit via the wires entering and exiting the unit. Some sources do mention about the center conductor having to be rf grounded but rarely do I hear of the grounds of wires entering and exiting the cabinet having to be rf brpassed to rf ground. I have had rf feedback problems for years because of this lack of info.
The audio wire ground is not rf-bypassed to the cabinet ground(rf ground), the cabinet itself. Capacitor 5 would bypass rf from the audio ground to cabinet ground if installed. In consumer units the audio ground may have to travel several inches or more before it is grounded to the cabinet ground, #1 and #2 in picture. During that journey the signal was able to interact with the rest of the circuitry causing problems such as hum, buzzing, static or the unit simply not operating. In most cases it is OK to ground the audio ground directly to the cabinet ground. If one is not familar with electronics it is always OK to use a .001uf capacitor to bypass the rf to rf ground.
The center conductor is also to be rf bypassed to rf ground with a .001uf capacitor. A capacitor must be used or the audio would be shorted out if one connected this wire directly to cabinet ground. If it is also not bypassed to cabinet ground, there could be the same problem as with the audio ground. Capacitor 4 bypasses rf to rf ground if installed. Some consumer units may have a capacitor rf bypassing the center conductor to circuit ground, #3 is an example. This is usually ineffective. This is because the circuit ground is several inches or more away from rf ground via a conductor the thickness of a wire.
REMEMBER! ALL leads(audio and ac power and dc power), the live ones and the grounds! entering and leaving the cabinet must be rf bypassed to rf ground(cabinet ground). It must be rf pypassed to within an inch proximity to the metal cabinet.
