Resistor influence on frequency respose

[Dealbreaker]

New guy question.  One of many. I'm looking for a layman, Cliff Notes version of how resistor values influence frequency response in a circuit.  Obviously they are needed in a tone stack (RC filter), but the influence resistors have on frequencies has never been clear to me.  Capacitors and inductors are more intuitive. Not so much as far as pots and resistors.  It would have helped if I took classes on this subject earlier in life, but I'm having a lot of enjoyment at Interweb Jr. College lurking and tinkering with my own stuff.  Hoping a kind soul here can shed some light.

[acheld]

Try this:

https://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-low-pass-and-high-pass-filter

Enter some values for both the low pass and high pass filters.   The Bode plot shows what happens.

[CascoSieg]

Also, Miller affect due to grid stoppers in combination with tube triodes.
https://www.valvewizard.co.uk/gridstopper.html

[Dealbreaker]

Thanks for the response.  I didn't know about the DigiKey resources. Very helpful. I am familiar with the Valve Wizard, but a lot of that information sails over my head.  I don't know what I don't know.  I need to wrap my head around AC resistance. Behavior in the DC realm is more straight forward. I understand how a capacitor is sort of a resistor of certain frequencies.  But how a resistor in an AC circuit can change a frequency is what I need to grip. For instance, how a grid stopper can strip off the high freq RF energy at the input, but not the lower frequencies.  Or does it affect them too?  Is it just a global reduction in gain that lowers RF frequencies at the anode?  Is it that tubes naturally amplify higher frequencies more easily and a grid stopper quells that?  Why not a grid-stop capacitor?  Bear with the amateur questions.  Its embarrassing for me to ask these things publicly, but I have searched and have not found anything I understand.  I don't have friends or family who have studied electronics. I appreciate everyone taking the time to guide me to knowledge.

[AlNewman]

For instance, how a grid stopper can strip off the high freq RF energy at the input, but not the lower frequencies. 

This is explained by the miller capacitance referenced above.

I recommend watching Uncle Doug's videos on tube amp design, he has a very informative series that breaks down a lot of the concepts in an understandable way for beginners. 

[sluckey]

A purely resistive circuit has zero effect on frequency response. IOW, all frequencies are affected equally. You must mix in some inductive or capacitive reactance to begin affecting different frequencies differently. Only then will you begin to influence frequency response.

[passaloutre]

Thanks for the response.  I didn't know about the DigiKey resources. Very helpful. I am familiar with the Valve Wizard, but a lot of that information sails over my head.  I don't know what I don't know.  I need to wrap my head around AC resistance. Behavior in the DC realm is more straight forward. I understand how a capacitor is sort of a resistor of certain frequencies.  But how a resistor in an AC circuit can change a frequency is what I need to grip. For instance, how a grid stopper can strip off the high freq RF energy at the input, but not the lower frequencies.  Or does it affect them too?  Is it just a global reduction in gain that lowers RF frequencies at the anode?  Is it that tubes naturally amplify higher frequencies more easily and a grid stopper quells that?  Why not a grid-stop capacitor?  Bear with the amateur questions.  Its embarrassing for me to ask these things publicly, but I have searched and have not found anything I understand.  I don't have friends or family who have studied electronics. I appreciate everyone taking the time to guide me to knowledge.

The tube has an invisible capacitor (three actually, they’re listed on the data sheet as “interelectrode capacitances”) from grid to cathode and grid to anode. The grid stopper then forms a low pass filter with these caps to (AC) ground. This is an RC filter, the same as any other you know about.

Plenty of tubes also have grid capacitors, we just usually call them coupling caps. The capacitor + grid leak resistors form a high pass filter going into the tube grid. There’s also the special case where the grid leak resistor is super big because it’s biasing the tube grid, but the same RC filtering rules you know apply.

[Dealbreaker]

Thanks all.  Very helpful. The "tone slope" resistor is what got me going down this road.  To the uneducated, I asked myself "How can a resistor alter frequency?" OK, so its the recipe of inductors, capacitors and resistors that steer the audio.  Now to really get my head around it.  I admire everyone's knowledge here, and the willingness to help. I was familiar with Rob Robinette's site, but not Uncle Doug.  Between those two, a total beginner gets a good start.  Its the deeper chapters like Miller capacitance which I have read about, but now understand (the concept anyway).  Load lines are also on my list, so I will probably bug the team with more questions down the line.  Thank you all.

[passaloutre]

Slope resistor is definitely a tricky place to start. It’s still the same RC filter rules you know and love, but that stack is the intersection of three different interconnected RC filters, so the math gets much more complicated.

[Merlin]

You need at least two components to make a filter. Essentially they form a potential divider. For example, in the RC filter below, at high frequencies the capacitor has a smaller reactance than at low frequencies. So the potential divider is 'turned down' at high frequencies, creating a treable cut response. It is the ratio between the resistance and capacitive reactance that determines at what frequency that 'turning down' begins.

[Dealbreaker]

Hi Merlin, thanks for chiming in.  I have been getting the hang of this concept with the use of the calculator acheld passed along from DigiKey.  It lets the user instantly calculate values to achieve a desired freq.  First thing I plugged in was typical cathode resistor/cap values and the resulting frequencies they pass.  Very enlightening.  I initially thought the cathode resistor was just bias for the tube, but there is also an audio "voicing" component when a capacitor is added.  And the tone stack interaction using various pot values really complicates things in my mind.  I have seen a tone stack calculator that helps visualize what different values of components produce, but without the basic concept of how resistors and caps create filters, it never really landed.  Voltage divider at certain freqs makes the most sense to me right now.  But I know this just scratches the surface.  Thanks again for the help!