Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Mike_J on January 22, 2016, 03:55:43 pm
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I ordered a $30.00 PEC dual 250K potentiometer thinking it would be much more accurate than the Alpha pot Doug sells for $4.50. I had purchased two of the Alpha pots from another source and each half of one of the pots was very close and I used it succesfully in a previous build. The other pot wasn't quite as good. That being the case I decided I would try the PEC dual pot because any company that would charge $30.00 for a pot and has precession in their name certainly would have very close tolerances. Oh how wrong I was.
On the PEC pot one side reads 245.1 and the other side reads 258.4. What I considered the bad Alpha pot was at least that accurate. If a company which pretends precision can't make a quality product at a price point of $30.00 then make it at a price point of whatever is necessary to be precise as their name implies.
Morale of the story is it would be much better to buy six Alpha pots and throw away any that do not read accurately (probably two or three based on my preference for accuracy) rather than spend $30.00 on a PEC pot. There would be a much better chance of getting something usable.
Thanks
Mike
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> one side reads 245.1 and the other side reads 258.4
+/-3%. Hardly shabby.
Every other part of the amp is 2% to 20% tolerance.
If you only care about end-to-end resistance, put a 4.762Meg resistor across the high side.
Pots are adjustable. The total value should not be too important, you will dial the setting you want.
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There are many specifications that go into an expensive, quality built pot. Tolerance is only one spec and your pot is well within the advertised +10% tolerance. Heck, your worse measurement is under 3.5%. Is your meter that accurate? Has it even been calibrated (traceable to NIST) to guarantee it's accuracy?
What is the intended purpose for this pot? PPIMV? I have some expensive milspec pots in a few of my earlier projects but I didn't have to buy them. I'd never buy a $30 milspec pot to go in a lowly guitar amp. :icon_biggrin:
http://www.precisionelectronics.com/0-40a-020a.html (http://www.precisionelectronics.com/0-40a-020a.html)
http://www.digikey.com/product-detail/en/KKA2541S28/KKA2541S28-ND/770962 (http://www.digikey.com/product-detail/en/KKA2541S28/KKA2541S28-ND/770962)
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I just got upset that a part costing more than six times as much as another pot I could have used is not more accurate than it is. Live and learn. I will never, ever buy another $30.00 potentiometer for one of my builds.
Thanks
Mike
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It wasn't a total bust then. :wink:
I like those cheap Alphas. Good feel and plenty good quality for a homebrew guitar amp.
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It wasn't a total bust then. :wink:
I like those cheap Alphas. Good feel and plenty good quality for a homebrew guitar amp.
Agreed.
Thanks
Mike
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Speaking of Alphas... I just bought some of these. More still available. Maybe someone here would like some of these cheap pots.
http://www.ebay.com/itm/Lot-Of-10-Alpha-1m-Audio-Potentiometers-/161950187655? (http://www.ebay.com/itm/Lot-Of-10-Alpha-1m-Audio-Potentiometers-/161950187655?)
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Speaking of Alphas... I just bought some of these. More still available. Maybe someone here would like some of these cheap pots.
http://www.ebay.com/itm/Lot-Of-10-Alpha-1m-Audio-Potentiometers-/161950187655? (http://www.ebay.com/itm/Lot-Of-10-Alpha-1m-Audio-Potentiometers-/161950187655?)
$0.80 per pot including shipping to my location is a good deal!
Added to my watched items for later purchase.
Thank you! :icon_biggrin: