Can anyone explain to me, the orange shield wire on PT?

[Guitarman18]

I've just taken delivery of a Heyboer 'Twin/Showman' PT for a D'clone build and see that it hasn't got the orange shield wire mentioned in a number of D'Clone schems. Is there a downside to not having one? If the shield needs grounding, why do some manufacturers not include it?


Many thanks in advance to anyone who can enlighten me on this subject. Yet another piece of the puzzle, missing from limited knowledge.

Cheers, Paul.

[Jana]

I think it is to confuse us. I just ground that wire on one of the PT mounting bolts and call it cookies.

I suppose there is a fancy explanations for it, like to feed harmonically aligned electrons into the shield to thwart the degeneration of the lamination crystal structure, but I was gone that day and forgot to take notes.

[Wayne]

...I suppose there is a fancy explanations for it, like to feed harmonically aligned electrons into the shield to thwart the degeneration of the lamination crystal structure, but I was gone that day and forgot to take notes.

Well, yeah, of course it does all that, but a shield on a PT also keeps RF & other noise from coming in off the line and getting capacitively coupled to the secondary. It's usually a single layer winding that runs the whole width of the core. It is grounded at one end (the end that is brought out as a lead), and open at the other (to prevent it from being "shorted turns".

Actually, the more I type, the more I like your explanation better

W

[Guitarman18]

Thanks for the response guys. So I assume that PT's without it are more suseptible to RF etc. noise? Is there a 'workaround' similar to the resistors thing for an artificial CT on heater taps?

[Wayne]

Not necessarily - if the first layer over the primary is a low voltage winding (like a heater winding ferinstance) it has the same effect.

As far as a workaround, I'm not sure.

W

[Structo]

Not sure about the shield lead but on the Heboer that I have in my D'Lite, it just has the center taps. Not noisy at all.

[Jana]

I think one workaround is to wrap the transformer in tin foil and connect that to ground with a 100 ohm resistor. Kind of like a virtual shield.

But seriously, I have never had a problem with transformers that didn't have it, most of the transformers I have used didn't have it either.

If you were really concerned I think the better approach would be to stop any rf from getting into the amp in the first place. How about a line filter on the power inlet. Corcom I think it is, probably many others too, make a line filter with little inductors, capacitors, etc. in a IEC style power plug. With that any RF or interference is stopped right at the power inlet instead of letting it bounce around in the power transformer and then trying to shield it from getting any further. I don't know, just rambling. Quite honestly, I don't worry about it, if the PT has the winding, I ground it, if not, no biggie.

[stoo]

Guys,guys guys.. where have you been!! It's for joining the flux capacitor to the plasma conduit! Sheesh!
Stew

[Guitarman18]

stoo wrote:

Guys,guys guys.. where have you been!! It's for joining the flux capacitor to the plasma conduit! Sheesh!

Will I have any issues with the space/time continuum vortex in my Delorian if I use the wrong brand of flux capacitor (what value? Do you have a Mouser code for that?)

Seriously guys, thanks for the responses, it's reassuring to know there are guys out there willing and able to help out with all the obstacles and pitfalls that amp building can throw up at you.

Cheers, Paul.

[Jana]

"...it's reassuring to know there are guys out there willing and able to help out with all the obstacles and pitfalls..."

And gals that wear tin foil hats!