Use the heater's CT - no need to create an artificial CT when you have a REAL CT. As for grounding you need to re-think/re-read this again, I'm not sure you're undstanding properly. Look at the pdf file while reading this slowly.
What is "star grounding"?
One of the best amplifier power supply grounding schemes is a "star" ground system, where all the local grounds for each stage are connected together (i.e.- that stage's own cathode resistor, it's bypass cap, grid leak resistor for that stage, etc.), and a wire is run from that point to a single ground point on the chassis, back at the power supply ground. Even better is a two-point star, where the power supply grounds (PT center tap, first filter cap ground) and output stage grounds (output tube cathodes for fixed bias, or cathode resistors for cathode biased, and output transformer secondary ground) are connected together and to the chassis at a single point, right at the ground of the first filter capacitor. The ground of the second filter capacitor, after the choke or filter resistor, is the star ground point for the preamp stage grounds. Use a local common point for each preamp stage ground, and run a wire from this common point back to the second star point. If two stages are out of phase with each other, they can share a common local ground, but don't use more than two stages per local common ground.
Why is it used?
The idea is to keep heavy power supply and output stage ground currents from flowing in the ground return of the low-level input stages. These ground currents can modulate the ground of the sensitive, high-gain preamp stages, and can result in hum or noise injected into the signal path. In particular, a capacitor input power supply filter can draw heavy currents for very short periods of time to recharge the filter caps at the top of each AC cycle. These currents need to be kept out of the preamp stage grounds.
A good analogy is to think of an amplifier power supply distribution as a river. All the small currents from the preamp stage feed into a larger river, which has the heavier currents from the output stage, and the still heavier currents from the power supply. You want each successive stage farther "upstream" from the power supply, so the heavy currents don't influence the smaller ones. In the case of the input jack ground, it is the farthest point upstream from the power supply, so it should be connected directly to the ground point of the first cathode resistor. If you give it an alternate path to ground through the chassis (or through a grounded pot), it will be influenced by ground currents in the chassis. Think of the first stage as amplifying the difference between the signal on the grid and the signal at the ground side of that stage's cathode resistor. If you have a long path back through the chassis to get from the input jack ground to the cathode resistor ground, it can pick up all sorts of stuff along the way. Keep it short, and use quality shielded cable, with the input jack isolated from the chassis, and the shield grounded at the ground side of the cathode resistor for the first stage.
Topic: Number of plate-loads per filter cap (Read 12130 times)