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Connecting valve shields to earth

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cr0wl3y

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Joined 2009
#1
Hi there,

Does anyone have any tips on what the best approach to connect valve shields (the metal "cans" that fit around the valves) to earth is? As my sockets are sitting on a turret-board and valves and shields are exposed through holes in the metal chassis, there is no "natural" physical connection between the shields and the metal chassis (and earth). To get effective shielding I need to connect them to the ground somehow.

Two options:

a. Each shield gets connected to ground individually
b. Shields are connected with each other (either with a copper strip or with wire and solder) and then connected to the ground bus at one point

Any advantages in either option, or shall I do what's easiest?

Thanks,
Nikos
 
#2
I would do whatever is easiest, noting that the bus idea works great provided it offers low rf impedance (large surface area) and goes directly to the chassis ground point, if such is not the case you may be slightly better off with short connections directly to the chassis.
 
#3
Most valve sockets have a central spigot which needs to be grounded, in order to reduce feedback between the pins. The shield would normally be grounded to the spigot via the valveholder metal. So I would ground each shield to wherever the valveholder is grounded. If your valveholders are not grounded then they should be. If they have no central spigot then just ground each shield to wherever the nearest ground is e.g. the bottom of the cathode resistor, whether star or bus ground.
 
#4
DF96 said:
Most valve sockets have a central spigot which needs to be grounded, in order to reduce feedback between the pins. The shield would normally be grounded to the spigot via the valveholder metal. So I would ground each shield to wherever the valveholder is grounded. If your valveholders are not grounded then they should be. If they have no central spigot then just ground each shield to wherever the nearest ground is e.g. the bottom of the cathode resistor, whether star or bus ground.
Click to expand...

There you have it, I had no idea the spigot should be grounded...how would you recommend connecting the spigots to ground? All together and then to chassis or each to its nearest point on the ground bus bar?

thanks,
Nikos
 
#5
Each should go to wherever that stage is grounded. Definitely not all together, as that could introduce coupling between stages. If you were using star grounding, then the spigot could be the star point for each stage, then connect each to the master star point. Don't worry too much about it, as it is just a screen and should not be carrying any signal current anyway. Simplest thing is to do what I suggested - connect it to wherever the bottom of the cathode resistor goes.
 
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