When building an amplifier with a fixed resistor (as opposed to using a 100K pot), where should the resistor be located?
Does it make sense to connect the 100K resistor from the center of the RCA jack to the ground on the jack?
Or, is it better to have the resistor connected to the terminal on the tube socket?
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Does it make sense to connect the 100K resistor from the center of the RCA jack to the ground on the jack?
Or, is it better to have the resistor connected to the terminal on the tube socket?
Bests to terminate the grid of the tube by putting the resistor at the tube socket.
If you were using a pot, it would be good to add a series grid-stop resistor at the tube socket (grid).
If you were using a pot, it would be good to add a series grid-stop resistor at the tube socket (grid).
If it oscillates you do. If it does not oscillate, it still may be unstable and the gridstop resistor will help.
I don't know of any hard fast rules about them, othere than a recommendation to always use them with high frequency tubes (TX tubes used for audio purposes).
I've seen a Marshall JCM800 with the high gain input 12AX7 oscillating. A gridstop resistor helped tame it.
Here is a good explaination on grid stop resistors:
Grid Resistors
I don't know of any hard fast rules about them, othere than a recommendation to always use them with high frequency tubes (TX tubes used for audio purposes).
I've seen a Marshall JCM800 with the high gain input 12AX7 oscillating. A gridstop resistor helped tame it.
Here is a good explaination on grid stop resistors:
Grid Resistors
Grid stoppers (in series with grid) will use the miller capacitance to form a low-pass circuit. You can easily set this for some arbitrary value above hearing, such as 35khz. It will reduce the chances of high frequency oscillation.
The grid resistor (grid to ground) is what the voltage to control the tube is developed across. Ideally, its ground and the cathode ground are identical. Any differences will be amplified as hum. Any long cable between the grid resistor and the tube pin may be seen as a series inductor and/or parallel capacitor (shielded cable). This may destabilize your amp, maybe not. I have seen RCA jacks with the Rgk on the jack and a wire to the pin in vintage equipment that was fairly stable.
Personally, I use a grid stopper at the input of every amp I make, and recently often at the power tubes' grids as well if necessary. The correct value depends on the tube being used, but for 'ax7, around 47k seems to have little effect on audio. Ideally use the smallest possible value that prevents oscillation, if you want to maximize Q.
The grid resistor (grid to ground) is what the voltage to control the tube is developed across. Ideally, its ground and the cathode ground are identical. Any differences will be amplified as hum. Any long cable between the grid resistor and the tube pin may be seen as a series inductor and/or parallel capacitor (shielded cable). This may destabilize your amp, maybe not. I have seen RCA jacks with the Rgk on the jack and a wire to the pin in vintage equipment that was fairly stable.
Personally, I use a grid stopper at the input of every amp I make, and recently often at the power tubes' grids as well if necessary. The correct value depends on the tube being used, but for 'ax7, around 47k seems to have little effect on audio. Ideally use the smallest possible value that prevents oscillation, if you want to maximize Q.
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