screened cable and shielded E88CC

[jerome]

Hi all,

I am still working on my first valve amp based on waarde's design
(http://headwize2.powerpill.org/projects/showproj.php?file=waarde1_prj.htm).

I wondering how two wire the two following thing:

1- Between the input plug (at the back of the box) and the pot (at the front) I plan to use shielded wire: I am suppose to connect the shield to anything for it to be more efficient?

2- The first tube a E88CC has a shield between the two half of the tube. It is recommended to connect this shield to ground. However I have been trying to understand and implement a star ground layout. As a result I have a ground point for the signal, a ground point for high volatge and one for cathode resistor those three point will then be connected to another ground point(where I don't know yet). So to which ground point would it be more suitable to connect this shiled ion the E88CC?

thanks

Jerome

 

[tiroth]

1. The shield should be grounded at one end. Sometimes this is worth playing with as to which end is grounded, or maybe ground one end and attach the other to ground through 100pF capacitor. All depends on your RF and EMI issues.

Leaving the shield unconnected could be worse than not having it.

2. Not certain...I'm not sure you want to attach antennae to your small signal ground point, so I would try one of the two other points.

 

[dhaen]

1) Normally the shield of the wire is a continuation of the "ground" from the input socket (which should normally be isolated from chassis) to the bottom end (anticlockwise end) of the volume control.
This should be viewed within an earthing policy.
The normal policy is "star earthing", where each ground wire is brought back to a single point, and then connected to chassis.

2) The shield of the E88CC should be connected to the single common ground point through it's own wire.

IMO a sensible common ground point for this project would be on-or close to the negative pins of C8 & C9.

Cheers,