on-board sho leads to question about pots

[boog]

so i decided to put a sho into an old guitar (washburn kcv-20), maybe get me to start playing it again. i decided to pull the tone control out so i wouldn't have to drill/route anything more than a hole for a toggle (and i never use the tone control anyway). i then decided to retain the tone pot itself as i don't have any that are the same physical size. the sho calls for 5k gain pot and the original pot is labeled (barely) as 500k. now things get tricky.

first of all the supposed 500k pot measures at about 350k. my limited knowledge has left me with the impression that resistors run parallel act like this: (r1+r2)/2. so it would seem this shouldn't work, but i figured i'd try anyway.  after a bit of trial and error i find that if i put a 5k1 resistor from lug 1 to 3 on the "500k" pot i get a reading of 4.95k. close enough for what i need. but that doesn't seem right at all. am i misunderstanding something?

after firing the thing up this way it works just fine, except there is no audible difference except in the last 1/4 or so turn of the pot, which is what i would expect (i think) if i used the original pot without a resistor in parallel. so why am i getting a lower reading? i'm so confused.

[markeebee]

I did a similar thing a while ago, and was similarly confused. This helped me out, pages 6 and 7:

http://www.esorol.com/assets/files/PDFs/Combining%20resistors.pdf

I ended up buying the right pot, guess you might need to do the same!

[the3secondrule]

ah found it:

http://www.geofex.com/article_folders/potsecrets/potscret.htm

this is pretty damn useful for pot tapering and all that!

[Hides-His-Eyes]

The taper will be pretty wild but it should "work". You' might have trouble finding a suitable pot depending on the guitar; any put that sticks out the wood is going to have a long thread on it.

[boog]

thanks guys! i'm afraid i'll eventually end up tracking down the 'right' pot just so it doesn't go from 'facemelt' to 'no change,' it's been a fun little project.