12-30-2018, 08:51 AM
willy,
treat it like any other shielded design your familiar with. treat it like the shield is an umbrella around the object you want to protect from external emi but i would not include the shield in the gnd side of the cap lead itself, i would gather the shield EMI and bring that path to an area not close to any tube pin or any trimmer cap etc ,, just find a clear open bonding point away from stuff. i use the term bonding loosely as there is a big difference between bonding and grounding.... think "tube shield"
i was under the impression the three leg cap was nothing more than a shielded cap.
i wrapped mine in a narrow band of automotive sticky back aluminum exhaust repair tape which included tinned solder wick braid hanging off to the side which starts under one of the early layers of foil. there may be some scientific reason as to why this method is not totally correct because if i used plain tin foil then the wraps of foil would touch each other making this better i think?. in my case i suspect that the automotive exhaust tape being separated by the layer of glue is creating some degree of capacitance itself, which isn't really good for a shield. my stuff's working so..............
i then added heat shrink around the cap which in my opinion only helped to friction seal up or keep pressure on the foil to solder wick connection. this would be more as a coupling shield i guess because the solder wick is not welded to the foil,, just touching.
if i had a do over,, i would have simply wrapped the cap in foil,, then wrapped the cap in solder wick and solder the wick in place but this might have damaged the poly cap.
i was looking around for copper braid you find in some coax to slip over the cap for the shield but could not find copper so i did this.
the difference here is my shield is not terminated to either end of the cap.
my Zenith 7H920 (with FM) schematic does not illustrate in print the concept that the shield is ever tied to one end of the cap so i made my shield like any other logical shield design,, just wrap the part and bond or ground this shield layer,, this way the shield acts as an antenna and shunts any EMI to chassis.
treat it like any other shielded design your familiar with. treat it like the shield is an umbrella around the object you want to protect from external emi but i would not include the shield in the gnd side of the cap lead itself, i would gather the shield EMI and bring that path to an area not close to any tube pin or any trimmer cap etc ,, just find a clear open bonding point away from stuff. i use the term bonding loosely as there is a big difference between bonding and grounding.... think "tube shield"
i was under the impression the three leg cap was nothing more than a shielded cap.
i wrapped mine in a narrow band of automotive sticky back aluminum exhaust repair tape which included tinned solder wick braid hanging off to the side which starts under one of the early layers of foil. there may be some scientific reason as to why this method is not totally correct because if i used plain tin foil then the wraps of foil would touch each other making this better i think?. in my case i suspect that the automotive exhaust tape being separated by the layer of glue is creating some degree of capacitance itself, which isn't really good for a shield. my stuff's working so..............
i then added heat shrink around the cap which in my opinion only helped to friction seal up or keep pressure on the foil to solder wick connection. this would be more as a coupling shield i guess because the solder wick is not welded to the foil,, just touching.
if i had a do over,, i would have simply wrapped the cap in foil,, then wrapped the cap in solder wick and solder the wick in place but this might have damaged the poly cap.
i was looking around for copper braid you find in some coax to slip over the cap for the shield but could not find copper so i did this.
the difference here is my shield is not terminated to either end of the cap.
my Zenith 7H920 (with FM) schematic does not illustrate in print the concept that the shield is ever tied to one end of the cap so i made my shield like any other logical shield design,, just wrap the part and bond or ground this shield layer,, this way the shield acts as an antenna and shunts any EMI to chassis.
