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Post subject: Fender twin presence potentiometer
Posted: Fri Jul 06, 2018 9:44 am
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Location: oregon
It is a 1K *REVERSE AUDIO* pot (also called reverse log or anti-log or "C" taper) Fender part number 047781, but it has been discontinued by Fender. Anyone know where to find one if these? Been looking for weeks. Any help is appreciated


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Post subject: Re: Fender twin presence potentiometer
Posted: Fri Jul 06, 2018 1:06 pm
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Location: Coastal Bend, Tx.
I've only seen 5k(50's) and 25k(60's) linear pots in the schematics I have.
What model year circuit do you have?
If 1k is what you want, Mouser has a bunch(179) to choose from.
https://www.mouser.com/Passive-Components/Potentiometers-Trimmers-Rheostats/Potentiometers/_/N-9q0ypZ1yzvvqx?P=1yzmq8c&FS=True


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Post subject: Re: Fender twin presence potentiometer
Posted: Fri Jul 06, 2018 4:01 pm
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I think he is referring to one of these amps.
http://el34world.com/charts/Schematics/files/Fender/Fender_twin_94.pdf

5 revisions of circuit boards with snap-in pots. Closest thing I could find:
https://www.futurlec.com/Potentiometers/POT1KCpr.shtml

Know nothing about the vendor.

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Post subject: Re: Fender twin presence potentiometer
Posted: Fri Jul 06, 2018 5:39 pm
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Location: Coastal Bend, Tx.
Thanks vinyl, now I've seen one theoretically of course.
Maybe this could be long wired on a back panel in that case,
https://www.mouser.com/ProductDetail/Alpha-Taiwan/RV16AF-10-15K-C1K-3LA?qs=8%252br4Hz5Xir8WNEChaHrrgg%3d%3d


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Post subject: Re: Fender twin presence potentiometer
Posted: Fri Jul 06, 2018 9:46 pm
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I think I'm going to have to rig one on to the PCB, since I can not seem to find a smooth shaft reverse audio snap in 1k pot. Fender emailed me back and they couldn't find anything either. I would like to keep it as original as possible, but it doesn't seem like that is going to happen.


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Post subject: Re: Fender twin presence potentiometer
Posted: Fri Jul 06, 2018 11:13 pm
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Aspiring Musician
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You didn't say what's wrong with the pot, but here is a last ditch effort.

https://www.youtube.com/watch?v=5qHflPHMu58

It may be beyond cleaning, but you may be able to use the carbon wafer out of a new pot with the shaft and wiper of your old pot. I think the same tabs that you unbend to dis-assemble the pot attach the snap-in bracket.

May not work, but might be worth a shot.

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Post subject: Re: Fender twin presence potentiometer
Posted: Sat Jul 07, 2018 7:17 am
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Hmmm that might be a solution, the pot is binding really bad, the shaft looked bent, its dirty for sure, but I didn't think about taking it apart. Guess that's the next step, it's already messed up, so it couldn't hurt. I'm fixing it for a friend. Noticed the presence pot binding and amp is really scratchy when you kick in the reverb. So I took it to my shop and was going to replace the pot, check the tank, and test the tubes.


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Post subject: Re: Fender twin presence potentiometer
Posted: Sat Jul 07, 2018 8:24 am
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Maybe buy the replacement pot and swap out the innards completely. This way you can keep the exterior mounting of the original housing.


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Post subject: Re: Fender twin presence potentiometer
Posted: Sat Jul 07, 2018 9:03 am
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You can sometimes carefully bend the shaft back to loosen the bind. It's soft metal that easily bends, but usually breaks when you bend it back. So you only straighten enough to lose the bind.
Now, the normal way of straightening will stretch the shaft out and finish breaking it off.
The trick I have been the most successful with is to use a channel lock pliers to grasp it down the length and push down and inward to compress the metal instead of stretching it. Its best to do it with the amp assembled.
If you wind up with a broken shaft, you can then pull off the resistance ring and install it on a similar pot.
The trick here is to disassemble the shaft and rotor of the new pot so you can use the old ring. The shaft is held to the rotor with a swedge on the end of the shaft that expands over the rotor. I use end cutter dikes to push the swedge back together. A small dremel cutter helps too. The idea is to remove enough shaft material to be able to slide the plastic rotor off the shaft without splitting it in half. Now you can mount the ring in between. After you reassemble it, don't try to swedge it back together. Bad things happen. Use epoxy or super glue.


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Post subject: Re: Fender twin presence potentiometer
Posted: Sat Jul 07, 2018 9:25 am
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All good advice. I'm going to see what I can do with straightening it, if it breaks then I'll swap the insides. Hopefully that works. I think I found a replacement 1k C taper on ebay as well, so I'll have a backup. Thanks all


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Post subject: Re: Fender twin presence potentiometer
Posted: Sat Jul 07, 2018 9:33 am
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Aspiring Musician
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Hopefully, the shaft isn't bent, there's just a bunch of crud in between the shaft and the bushing. Clean it out, and then check the bushing for scoring and the shaft for burrs. Roll up some emery paper and "hone" the bushing, and remove any burrs from the shaft. Clean off any grit, and lube lightly.

I saw a video that showed exactly that, but I couldn't find it.

Good luck, and let us know how it turns out.

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