...a triode and instead of going silent, it buzzes and hums? It's wire is picking up some RFI, but when I ground it, it actually gets worse.
What am I not thinking of here?
What Does It Mean When You Ground the Grid of...
Moderators: pompeiisneaks, Colossal
Re: What Does It Mean When You Ground the Grid of...
Where are you grounding it? There are a lot of different grounds in an amp (they can even be a different potentials, since "ground" can be relative to the specific circuit). Any ground connection from a large current source will generate a signal if there's even the slightest resistance (and there always will some resistance).
Re: What Does It Mean When You Ground the Grid of...
it's making a ground loop.
consider the tube has multiple ground connections. according to the cathode, which is "ground" as far as the tube is concerned, you have ground at one potential. the grid controls the flow of electrons to the plate. so if it's humming or buzzing when you "ground" the grid, then what is happening is COMPARED TO THE CATHODE, the grid has some signal on it.
so the point is, the cathode could actually be the one with the hum.
anyway try grounding the grid at the same exact turret or ground location as you ground the cathode non that same tube. you will want to limit loop area so you want to run the wire that grounds the grid as close to the chassis ground plane as possible.
you might chopstick it a little bit and see if moving the grid wire around changes the hum. in the direction where the hum increases, you are increasing the ground loop area (area contained within the looping ground conductors). in the direction where the hum decreases, you are reducing the loop area. reroute that wire so that reduces the loop area to nearly zero and the hum likely will go away.
anyway...
so many amp builders and designers don't really consider how current is flowing in their amps, and just get lucky to not have ground loops and hum problems. not such a huge deal at audio frequencies but it's the difference between being able to sell a product or not when you are working in the EMI/EMC field with radio frequencies.
consider the tube has multiple ground connections. according to the cathode, which is "ground" as far as the tube is concerned, you have ground at one potential. the grid controls the flow of electrons to the plate. so if it's humming or buzzing when you "ground" the grid, then what is happening is COMPARED TO THE CATHODE, the grid has some signal on it.
so the point is, the cathode could actually be the one with the hum.
anyway try grounding the grid at the same exact turret or ground location as you ground the cathode non that same tube. you will want to limit loop area so you want to run the wire that grounds the grid as close to the chassis ground plane as possible.
you might chopstick it a little bit and see if moving the grid wire around changes the hum. in the direction where the hum increases, you are increasing the ground loop area (area contained within the looping ground conductors). in the direction where the hum decreases, you are reducing the loop area. reroute that wire so that reduces the loop area to nearly zero and the hum likely will go away.
anyway...
so many amp builders and designers don't really consider how current is flowing in their amps, and just get lucky to not have ground loops and hum problems. not such a huge deal at audio frequencies but it's the difference between being able to sell a product or not when you are working in the EMI/EMC field with radio frequencies.