500k vs 250k pots -- what to expect?

They will sound hotter and brighter.

I recently finished a Tele build with a Lil’ 59 (bridge) and the vintage stack (neck). The SD wiring diagram called for 250k pots. I went with a 300k volume pot for just a little more “umph” in the output. This worked out well for me.

It’s the volume pot that makes the most difference.

I haven't experimented enough with stacked pickups to say if I prefer one over another.

When Strat pickups are wired up with 500k, they can sometimes sound kinda bright and brittle. Fun fact: many import single coil guitars come with 500k pots. So, if you've played a Squier or similar and found it a bit overly sharp and maybe blamed it on the ceramic pickups, the pots might actually be to blame.

If you can get your hands on some alligator clips and resistors, you can find out what you're missing out on later. Wire it up with 500k, then you can put the alligator clips anywhere that is convenient, one on the lead and the other on the ground. It'll be noisy, but that's okay. Clip in a resistor, and it'll be parallel to the volume pot load. So, if you have a 500k pot and put in a 470k resistor, you'll have something pretty darn close to what a 250k pot would give you. If you have alligator clips but no resistors, you can use the two outer lugs of a spare 500k pot. This is a lovely trick for, if nothing else, just having some actual sense experience for what different pot values do instead of just listening to a yahoo like me on a message board! You can also wire in the resistors permanently if you stumble on a combination that works really well but you can't duplicate with a single pot swap. You can even do this at the switch to give different loads to different pickups, a very handy thing when combining humbuckers and single coils.

Another fun thing is if you have a multimeter you can measure pots very easily and find out how far off tolerance they are. Sometimes purposely selecting them high or low can be fruitful.

The Duncan Vintage Stack pickups are designed to sound like single coils, which they do very well. If you don't think you would like standard tele pickups with 500k, then don't start there with these ones. They may technically be stacked humbuckers but that's not a reason to go with 500k pots.

And remember if you do decide that 2 x 350k is too dark, you can always try one 250k and one 500k. If that's still not bright enough, switch the second pot.

With standard wiring (ie not 50s arrangement), except at low tone settings, the vol control track's resistance and the tone control's resistance are effectively in parallel, ie over the relevant frequency range, the cap's reactive impedance may be regarded as a short.
Consider a typical 47nF tone cap; its reactive impedance will be 250k at 13.5Hz, 25k at 135Hz, 2k5 at 1k35Hz.
So with a 250k vol and 250k tone pot, the loading on the pickup is 125k or less, ie the parallel combination of the vol and tone control. The instrument cable's capacitance, and amp's / pedal's input impedance will then be in parallel with that.

A guitar pickup is an LCR series resonant circuit, it has a massive resonant peak, typically around a few kHz; its output and impedance will be greatest at that resonant peak.
The load on the pickup acts to damp down that resonant peak (akin to putting gaffa tape etc on to the skins of well tuned drums, to reduce their resonant 'boingyness'). Hence as the tone control is turned down from max, the pickup's resonant peak gets progressively damped down. The interaction of the tone cap with the pick up don't occur until very low tone settings.

Some great info www.buildyourguitar.com/resources/lemme/index.htm
www.gitec-forum-eng.de/wp-content/uploads/2019/03/poteg-9-1-potentiometers.pdf


If the pickup manufacturer suggests a wiring arrangement / values for the pots, that's probably your best starting point 

If I remember correctly, the pot values will alter the height (and possibly Q?) of the resonant peak, while cap values will shift the frequency down as you go up in value. To my ears, this is why it can be problematic to describe higher cap values as "brighter" or lower ones as "darker" because typical passive pickups have a resonant peak in the upper, treble ranges (active pickups usually have it up above our range of hearing, usually the "hotter" the pickup the lower the resonance, but lots of stuff goes into this), and when you shift it down with a higher cap value, it can move into the upper midrange which will SOUND brighter to a lot of ears because it hits that high vocal, honky, Fran Drescher area, even though the actual Hz will be lower. I've had people swap out humbuckers in guitars because they're too "bright" while there's a .047uf cap in there just to get something even more "bright" despite what the descriptions from the pickup manufacturers say. Get a .022uf cap in there and it mellows right out. There's an entire generation of guitars that came forth from one of the "build your own guitar" books that was big on using .047uf caps with humbuckers, along with an obsession with star grounding, Carvin is one that comes to mind.

I'm not sure if I'm recalling all of my information correctly, but it does go to show that there is no substitute for just trying it and seeing how your ears like it. It defies logic sometimes which tells us there's something deeper than rock star science.

0.01uF and above, the particular value of the tone cap is pretty much immaterial to the action of the tone control, until it is adjusted below a fairly low resistance, typically less than 10% of its full track resistance. So less than ‘5’ or halfway on an audio taper pot. Or less than about ‘2’ on my Les Paul that’s got linear taper pots
So for the many guitarists who never turn their tone control below ‘10’ (or even below maybe ‘7’ really), the particular value and characteristics of tone cap/s don’t matter a damn, as the tone cap could be replaced by a wire link without any change in the response.