Brandon B

I just replaced the potentiometer in the pedal with the one from the website above. It was a little tricky. First, unsolder the old slider, and remove it. Second, the slider arm is too fat to fit inside of the metal arm, so I secured it in a vice and used a file to trim the fat off the top and bottom of the slider arm. Third, the potentiometer's install tab is on the wrong side. I used a 1/4" chisel to pop a small slit in the plastic plate so the tab could go through. Epoxy was my backup plan, but the chisel worked. Then I bent the tab so lock the pot in place on the plastic board. Fourth, I gently bent the prong to the side so it would touch the connecting wire. I pressed the connecting wires into place that attach the slider pot to the trim pots. The connecting wires are stiff wire, not multi stranded, so you can move them into place and they will stay put. Fifth, the connecting wires had enough solder on them to reattach them, but I put a dab of solder on top, just to be sure. I found when I ran the first test, that I had to really tighten up the Allen set screw on the metal arm, because the old pot is very easy to slide compared to the new one. I reset the trim pots and it works perfectly. Frankly, I'm surprised at how easy everything went together. I'm sure there are pots that might have the tab on the right side and a skinnier slider arm, but whatever. The wheel moves sooooooooooo beautifully. I've used a bunch of Brents, but I've never seen it ramp up and down so smoothly. I'm happy with the results.

AH! that makes so much sense. I forgot that the rest of the world uses 220V at their outlets.

I'm pretty sure that the drawing you have posted (not totally positive) is for the very first generation of wheels. I think they were 220V. Mine is from mid to late 70s which I think was the second generation, it runs on 120V. The trim pots are connected, one in series and one in parallel, to adjust the stop position and the high end speed of the pedal. I was told that a 1M ohm potentiometer should work for this application, If I can't find a 750k ohm. Finding a 750k with the correct shape, and PC connection has remained elusive. If anyone finds one, let me know. My grandfather was an electrical engineer back in the 50s - 80s and I remember just about any motor with enough torque to spin 75lbs while someone is pushing against it was 220V. He had shelves and shelves of electric motors he would let me play with. I wonder if Brent would have used a 220V motor originally, as it was the "go-to" back then. with some more playing around, maybe Brent found that they could use a 120V successfully... I don't know, just a thought.

I measured it at 0 - 0.75M ohms from top to bottom. Its definitely linear. For anyone who is checking the resistance, ohm meter must be set to M (I have a blue point meter and is says 2M). There are three prongs, on the pot, two next to each other and one at the other end. measure from one of the two that are next to each other, to the prong at the other end (that isn't connected to anything). It should give you a pretty accurate reading.

sorry here it is if you still need it https://www.surplussales.com/Potentiometers/Slider/Slider-1.html

I'm going to buy the one on this page https://www.surplussales.com/cgi-bin/cart.pl labeled as: (RCV) BX8195-0 We will see what happens!

Here is that explanation about potentiometer resistance: The pot makes a voltage divider that feeds the analog input. Vout = Vin * R2/(R1+R2) where R1 is the resistance between Vin and Vout, and R2 is the resistance between Vout and Ground. If the knob is halfway, then R1 = R2, so the equation simplifies: Vout = Vin * R1/(R1+R1) so with 5K: Vout = 5V * 2500/(2500+2500) = 2.5V. and with10K Vout = 5V * 5000/(5000+5000) = 2.5V. So the overall value of the pot doesn't really matter. Where the value does come into play is how power it dissipates. Power = Current x Voltage, or P=IV. Current = Voltage/Resistance, so a 5K pot with 5V will have 5V/5000ohm = .001A, 1mA going thru it. Power = .001A * 5V = 5mW, which is not much, but might be an issue for battery powered operation where long ontime is a concern. In which case a 10K pot might be better.

Thanks for all the replies. I haven't had a chance to open up the pedal again and take pictures, but there are pictures online that show what it looks like. I was posting about this on a electronics forum, and some people didn't seem to think the resistance mattered, just as JohnnyK had stated. They said that any resistance will work, but that the power will dissipate differently for different resistances. They had some fancy equations to describe the relationship... I can find some slide pots that are the same size as the old one, so I'm thinking that I am going to try buying one and putting swapping it. Worst case, I'm out $2. They said it wouldn't have any effect on the motor, somehow... I was able to clean it thoroughly and that seems to have helped significantly, however, I was told that cleaning is usually a temporary fix with diminishing rewards over time. Seeing as this is mid century technology, I figured it would be as easy to fix as working on my stereo. Frankly, I'm amazed at how hard it is to find this part. I was tipped off that manufactures sometimes buy parts from other countries (from companies that don't sell in the US) in order to hide their source, so people can't buy component parts. Who knows whats going on here, but it sure is annoying.

I'll look at those websites. I checked parts express already, and didn't find anything that matched. Thanks for the info! Here are pictures of the old and new potentiometers. As far as google and every online store I have tried, the numbers on the side mean nothing.

I've familiar with the pedal construction. I was hoping someone who has experience with Brent pedals could tell me what the difference between the B pedals from the 70's and the new replacement part is. It looks VERY similar on the parts sales page. The new potentiometer is very similar to the old one in looks. but not sure if the dimensions are the same. the old one is 2'x7/16'. I measured the resistance at 0-0.75M Ohms. Tech support won't reveal any of the specifics, since they are, understandably, trying to cover their profit margins. The real idea here is to find the potentiometer that Brent uses, either currently or "old, new stock" and swap it out. I have looked all over the web and haven't been able to find a straight part for part swap. (~$5) If it is truly not possible to swap out the pot, then I was going to buy the new replacement pot assembly and modify or remove and replace the slider pot, if its the same dimensions. (~$90)

I have a model B from the 70s, and it seems to the potentiometer replaced. I was thinking I’d buy the assembly from Amaco, but they said it wouldn’t fit in my pedal housing. Slide pot ID number is ZM4509 137/539, I can't find anything that is even close to this number online. Does anyone know what the modern equivalent is? wouldn’t fit how? Could I modify the assembly to fit the old pedal? I also figured I could remove and solder in a new potentiometer. I have looked everywhere online and called a dozen people but can’t find the $1.50 potentiometer for sale. Does anyone know where I could get one? $250 seems about right for the whole pedal I guess, but not for $5 worth of parts. I must be able to get these simple electronic components somewhere, right? thanks!