Oscillations problem help

[Helmholtz]

To minimize inductances, all wires connecting to the grid and plate pins as well as ground wires should be as short as possible.

[catalin gramada]

Thanks. There are. I did the correction on my layout in respect with VK sketch. Is in order like this please ? Still not clear if 1M grid leak is necessary from a grounding perspective?

[vintagekiki]

... why 1M grid leak resistor is need it as time 47k input is shunted to ground ...

The resistor 1M prevents the input from floating when input is no connected, and sets the input impedance, to be on high relative to the source impedance.

Useful link ¹⁾

https://robrobinette.com/Amp_Stuff.htm

[catalin gramada]

1. The input is not floating. It will be shunted to ground when not in use. 2.Even by an open contact by accident the current is well limited to not endanger the tube. 3. Is not clear how setting in grid a resistor to the ground you get a higher impedance relative to the source as we are talking about a guitar pickup impedance series with 47k of the stopper relative to impedance of the grid which is theoretical infinite...This is a must for sources which contains DC components and should be isolated by a cap...then it need a grid reference for the tube... not my case

[vintagekiki]

2. How tube get bias voltage?

[Helmholtz]

1. The input is not floating. It will be shunted to ground when not in use. 2.Even by an open contact by accident the current is well limited to not endanger the tube. 3. Is not clear how setting in grid a resistor to the ground you get a higher impedance relative to the source as we are talking about a guitar pickup impedance series with 47k of the stopper relative to impedance of the grid which is theoretical infinite.

Agreed, but I consider the 1M grid leak resistor a "safety" measure in case some (active) device is connected to the input, which doesn't provide the necessary DC path to ground - though that's probably rare.
And sometimes switching jacks fail.
What's the problem with adding it?

I would connect the 47k grid stopper directly to the socket pin.

[catalin gramada]

2. How tube get bias voltage?

By cathode which is positive to ground. The grid is dc related to ground from the jack switch when nothing plugged or through the volume pot of the guitar when some is pluged in. A floating grid should be possible by accident with the guitar unpluged which is a frequency scenario by players practice, but think no worries as the current is well limited away to endanger the tube.

[vintagekiki]

the current is well limited

With what current is "very limited"

[vintagekiki]

Colleague so you are a genius.
When you have the answer for everything, why are you wasting your time here?

Useful link

#16
#17

[Helmholtz]

Colleague so you are a genius.
When you have the answer for everything, why are you wasting your time here?

Useful link

#16
#17

No personal attacks, please .

Tube current is limited by plate resistor and the grid leak resistor is only required if there is no other DC path to ground.

[catalin gramada]

Colleague so you are a genius.
When you have the answer for everything, why are you wasting your time here?

Useful link

#16
#17

I expect to get an answer at what I didn.t know, not what I allready state. You are talking about a grounding problem which is wrong related to my layout in you oppinion: "The ground loop definitely exists." I don't see it and I expected to get an answer. You send me a layout and thanks for that, but still I want to know where I do it wrong. I take it out the shielded wire from equation to make it simple and replaced by normal wires to avoid reactive coupling. But still don't see the grounding loop where you talking about so pretty please ask to show me where I get it wrong.
I posted my layout, just indicate me ...: the current path which create a ground loop from point A to point B because I don't see it.

[vintagekiki]

No personal attacks, please .

You are right but in #56 no one has been personally attacked.
1)
How tube get bias voltage when the jack is open and no grid leak resistor. (schematics)

[catalin gramada]

You are right but in #56 no one has been personally attacked.
1)
How tube get bias voltage when the jack is open and no grid leak resistor. (schematics)

The jack will be open just with a guitar pluged in. The dc grid reference will be established through volume pot of the guitar and guitar cable.

[vintagekiki]

The jack will be open just with a guitar pluged in. The dc grid reference will be established through volume pot of the guitar and guitar cable.

Question
What happens if is an effect between the guitar and the input jack, for example

[catalin gramada]

Question
What happens if is an effect between the guitar and the input jack, for example

Then a grid leak resistor will be necessary, but is not my case, I omitted the grid leak from circuit just for this reason. Is not necessary for my aplication so I didn't putted in.