Determining the resistor value on a treble bleed for gain pot

[12AX7]

In my guitars i use the typically specified 220k in parallel with a cap on the volume pot. But what about in a amp? First, they never seem to specify a resistor of the same value as the pot value in every case. I mean, they always specify 220k without mentioning whether you would want a different value on say a 500k, or in some cases a 1M which some use. The gain pot in question is after the first stage of a 3 stage cascaded preamp and it's a 1M pot. I have a 250pf cap on it, but it seems like a 220k resistor in series doesn't help much. Is there a general rule about what value to use?

[HotBluePlates]

You've lost me a bit with the change from "resistor in parallel" to "resistor in series". There's also no set rule for how to set up a "treble bleed" or "bright cap". It's all about getting a sound you want. A parallel resistor is often about faking a particular pot taper, while a series resistor is about taming the intensity of the treble bleed.

We could derive an equation, and talk what specific frequency is being affected x-amount, but do we necessarily know what number to shoot for?

A faster way is a (maybe homemade) cap substitution box with a variety of pF-range caps, and place a maybe 250k-500k pot in series, wired as a variable resistor. Set the pot for no resistance, and dial the cap box until you get the range of treble/mid boost you want. Start turning up the pot to tame the amount of boost. Go back and forth as needed to zero-in on the sound you like best.

When done, note the value cap selected and measure the resistance between the pot lugs. Or if you rigged up a box at home for repeated tweaking of this type, maybe you have measured and marked resistances on the panel of the box, and can read off the value from that. Choose the closest standard value, or if it "has to be exactly that" select a pair of resistors that provide that value when paralleled.

[Tone Junkie]

Thanks HotBluePlates thats some good stuff right there never thought of it. I feel the need to build another cap box.   
Thanks Bill

[12AX7]

Sorry, that was a typo. I mean parallel. I have tried it with a series resistor tho, and did in fact use a pot at one point. I think in a guitar at least a parallel resistor works better to my ear than reducing the amount of effect like a series resistor does. I guess a parallel R changes the taper in a way that seems to keep a better balance of low range to high, so i figured that would be good in a amp too. But i wondered if a different value would be best. Yes, i can experiment but it's one of those subtle things that you try and finally figure out whether it works good or not after day or weeks or even months. So asking here i hoped I may find whether theres a typical value to use with a 1 M gain pot with a 250pf cap in an amp's gain stage.