Pot specs

I am trying to figure out the specs of a few pots. One is labeled 15A50K 9637L, the other pot is labeled B20K 9367L. I am assuming the resistance values are 50k and 20k respectively, and both are linear. What are the power specs though?

Thanks!

What type of this device are these potentiometers from?

I’m not sure we will be able to locate the power rating for these unless we can locate what series these are from.

You may have to contact the original manufacturer of the device to see if they can tell you that information.

Hi Travis,
These are from an amplifier for an M&K V-75 Mark II Subwoofer. One pot handles the gain, the other, the frequency cutoff. Unfortunately, the sub is no longer made and the company no longer consists of the original ownership and designers.

Similar products have power ratings ranging from around a quarter-wattt to several watts, depending mostly on the type of conductive element used. Typical audio gain/frequency controls are low-power circuits however, so I’d not expect power rating to be a huge concern in selection of a replacement.

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Gain pots in audio circuits are usually logarithmic taper not linear.

If the pot still works mostly, you can verify linear vs. logarithmic with an ohm meter. A linear pot will read ~1/2 Rt at the mid point. A logarithmic pot will not be anywhere near 1/2 Rt at the mid point (typically 10% or 90%). See the following link for more info on taper: http://www.resistorguide.com/potentiometer-taper/

Most modern audio circuits put only a small amount of power through the control pots. If the pots still mostly work you can get an good idea of the power rating by intentionally burning them up with an adjustable voltage supply. Rotate the wiper to one end and attach the power supply between the wiper and the other end. Increase the voltage while watching the current and when the pot starts to burn out you’ll see the current drop. Then calculate the power that burned it out (W=V^2/R).

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Thanks PaulHutch for the great info! My gain pot is indeed a logarithmic taper pot.

Hello. I have an M&K sub with the exact same 2 pots. Did you have any luck finding replacements? If so, were you able to get your sub up and running? I replaced the gain pot with a 50k audio taper one I found on Amazon (https://www.amazon.com/gp/product/B002IA8BCO/ref=ppx_yo_dt_b_asin_title_o05_s00?ie=UTF8&psc=1 ) that was bigger than the original, but has been said to work correctly. I had to drill out the mounting hole a bit, then installed it with wires in same place they were on old one. The gain dial then worked, but was backwards (had to turn it counterclockwise to make the sub louder instead of clockwise) and the gains were too extreme. Just barely moving the gain knob made the driver stress like I had just turned it from 1 to 10. Also, it would not work when the speaker size settings on my receiver were all set to Large. As soon as I set any of the 3 to Small, it worked (but still not correctly, same as previously stated) So I switched the 2 outer wires (green and white) and had same results. I’d like to replace the other pot as well, but not sure if I want to try another one of the larger ones from Amazon. Here are pics of the 2 original pots as they were when I first saw them. Same wiring as yours I believe.

Hi Apache2223,
Volume pots are typically exponential such as KA5031S28-ND , but linear pots would also work fine in volume applications. Some people actually prefer linear pots in some volume applications as you get more precision when setting a volume, where exponential pots are quicker to turn the amp up without having to rotate it a full turn. When the volume is backwards, and level too extreme, it is wired on the wrong side of the pot. You could move your green wire to the other side of the pot (opposite outside leg) and this should fix the volume issue.

Frequency control knobs are linear, such like 987-1660-ND | 480-5892-ND options.

Hello Ryan, thanks for the reply. I actually did switch the white and green wire and now when I start from say volume 1 going to 10, there’s no change until about 8, then it gets ALOT louder immediately and the driver starts moving outward way too far. So I messed with the settings in my receiver, where you specify Small or Large for speaker type…there’s Front, Center and Surround and when all are set to Large, there’s not much sound coming from the sub, but if I switch any of the 3 to Small, it gets very loud and sounds horrible. I have Extra Bass turned off, Volume Trim set to 0.00 and the Bass Tone is also 0. I ordered the 2 big caps on the Amp thinking maybe that’s part of the problem. They don’t look bulged, but one has the paint chipped off the top of it. The other knob on the back of the sub is the Low Pass Filter. I replaced it’s pot as well, but it doesn’t seem to change anything when I adjust it. I noticed one of the frequency control knobs in your link is 2W and the other is 0.5W. I’m not sure what wattage I need because when I look up the numbers off the old Pot (B20K 9637L), I don’t find anything except this page.

Hi Apache2223,
This may be a separate issue aside from the pots. The wattage requirement of the pots is unknown, but would think this would be negligible as the main reason large pots are used in this application is for panel and knob mounting, not necessarily for power handling.