Who Posted a RFI Reduction Circuit for a Marshall Amp a Whike Back???

[T-Rex]

At our last house in Indianapolis, we were maybe a half mile at most from the tower that broadcast Country stations. Without these grounding washers I could "hear it all" quite clearly. Putting those washers in snuffed them right out. And the RFI was worse the lower in the house that I went, horrible loud in the basement, where I had the shop set up. Go figure.

 

[Amp Mad Scientist]

I use the clip on grounding washer, (got a few from TubeDepot). Add a .01uF cap to ground from the sleeve tab and radio stations are gone and the tone doesn't change.

Grounding Washer

It's not really clear what the circuit is from the photo you posted.
It's not really clear where this connects into the circuit.
Is that the input jack, speaking of the photo?

 

[Amp Mad Scientist]

Here's the Marshall schematic with RFI circuit shown far left center...

View attachment 81062

Are you talking about the resistor / capacitor in parallel between circuit ground and chassis?

Is that what you are talking about?

 

[T-Rex]

It's not really clear what the circuit is from the photo you posted.
It's not really clear where this connects into the circuit.
Is that the input jack, speaking of the photo?

View attachment 81083

Yes the grounding washer snap fits onto the barrel of a Cliff type jack. There are two tabs that stick up in the air off of the grounding washer. The .01uf cap is soldered to one of those tabs and the other end of the .01uf cap solders to the sleeve ground of the input jack. Since the washer has teeth that bite into the chassis, the input jack sleeve ground now has a signal path through the .01uf capacitor to bleed that induced signal to ground at the closest point of entry, the RFI signal that has induced itself onto the guitar cable.

 

[Amp Mad Scientist]

Yes the grounding washer snap fits onto the barrel of a Cliff type jack. There are two tabs that stick up in the air off of the grounding washer. The .01uf cap is soldered to one of those tabs and the other end of the .01uf cap solders to the sleeve ground of the input jack. Since the washer has teeth that bite into the chassis, the input jack sleeve ground now has a signal path through the .01uf capacitor to bleed that induced signal to ground at the closest point of entry, the RFI signal that has induced itself onto the guitar cable.

OK that's beauty.
But it only works on non chassis grounded input jacks. (like a Cliff Jack)
Like a Marshall, etc it will work.
But old Fender does not have that isolated jack.

 

[Inspector #20]

Are you talking about the resistor / capacitor in parallel between circuit ground and chassis?

View attachment 81084 Is that what you are talking about?

Yes. On the PCB it's marked "RFI SUPPRESSION. "