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DIY Stompboxes => Building your own stompbox => Topic started by: morganpedals on June 08, 2004, 01:33:18 PM

Title: Help finding potentiometers
Post by: morganpedals on June 08, 2004, 01:33:18 PM
I am working on replacing 3 pots on my Marshall Bass Amp. I have been unable to find the exact replacements from Mouser, Allied, Parts Express, etc. I found a pot from Bourns - PDB 18 series - that fits perfect. Here is the spec sheet. http://www.bourns.com/2/pdfs/PDB18.pdf

The exact part number would be PDB18 1-K420K-103A

It is a PC Mount Audio 10K pot. The shaft is 20mm, vertical pc mount pins, knurled shaft.

Does anyone know how I could find this pot or something similar? I called Mouser, and they told me that I would have to order 1000. They didn't have anything else that would fit.
Title: Help finding potentiometers
Post by: RDV on June 08, 2004, 01:46:30 PM
http://www.tubesandmore.com/new/scripts/silverware.exe/catalog@d:/dfs/elevclients/cemirror/ELEVATOR.FXP?PAGE=SUBCAT&SEARCH_TREE01=POTENTIOMETERS&SEARCH_TREE02=MARSHALLSorry, no 10K though.

Regards

RDV
Title: Help finding potentiometers
Post by: john1056 on June 08, 2004, 04:19:22 PM
Couldn't you use one these pots (e.q. 22K) and just solder a resister in parallel with the 1 and 3 lugs to get a lesser value?  I've been doing this when I bread board circuits.  I have a few 1Ms and I just use a resister value close to what I want (100K, 250K etc.)
Title: Help finding potentiometers
Post by: Brian Marshall on June 09, 2004, 02:02:25 AM
Quote from: john1056Couldn't you use one these pots (e.q. 22K) and just solder a resister in parallel with the 1 and 3 lugs to get a lesser value?  I've been doing this when I bread board circuits.  I have a few 1Ms and I just use a resister value close to what I want (100K, 250K etc.)

It is actually a little more complex than that, especially if you are using it as a potentiometer, and not a rheostat (i.e. using all 3 lugs.

if you set the whiper in the middle with a 1 meg pot, you will see 500kohms to lug one, and the same to lug 3, but if you add a resistor (ie 10k) to 1 and 3 now you will see about 250k resistance to lug 3 or 1 from the whiper.  you want to see 5k.... you actually have to add a resistor from 1 to 2, 1 to 3, and 2 to 3.  the resistors on the whiper should be smaller, and the 1 to 3 resistor should be larger.  the math is not that complex, but it is pretty long.  I dont know it off the top of my head, but if i thougth really hard, and if it werent so late i could probably pull it out of my @$$.

brian