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Author Topic: Small Wonder 30+ gain control problem  (Read 507 times)
W1JKA
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Posts: 1619




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« on: October 29, 2012, 10:48:25 AM »

   Finished building an SWL 30+ qrp transceiver,everything with exception of the 5k gain control works fine and I have had several qso's with it.Problem with the gain control is that it is not a steady increase,it goes low volume for about 3/4 of range then immediately to high volume for the last 1/4 of range(no steady increase in volume). I have tried switching leads around on the pot ears and rechecked solder joints on the pc board and the only result is same problem only in opposite rotation of gain control.I am obviously overlooking something basic here and before I go probing around in the amp circuit and chance shorting something out I would appreciate any advice.I have not ordered another 5k pot yet, if you think mine might be bad.Thanks     Jim
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W5FYI
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« Reply #1 on: October 29, 2012, 10:55:47 AM »

Just a guess, but you may have gotten an audio taper pot instead of the linear taper called for. Radio Shack should have a quick fix. GL
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K4KRW
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Posts: 98




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« Reply #2 on: October 29, 2012, 08:50:17 PM »

I agree.  You probably have the wrong taper.  The gain control on your rig is indeed supposed to be linear taper according to the instructions.  Set the potentiometer at it's mid position and measure the resistance between the center lead (wiper) and both ends.  If you get approximately the same reading on both sides, it is linear.  If you get substantially different readings it is probably audio taper (logarithmic).  You can also often tell by markings on the part.  Parts marked for the U.S. market usually have an 'A' if they are audio taper and a 'B' if they are linear taper.  So, the pot I just bought for my OHR100A to replace a damaged volume control is marked B10K.  So, mine is a 10K Ohm linear taper pot.
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W1JKA
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« Reply #3 on: October 30, 2012, 10:58:29 AM »

      Thanks to both you gentlemen problem now solved with new pot from Crap Shack.Now in process of combining the SW-30 with my NeScaf filter,Texas Topper qrp amp and combo amp/speaker from old computer into one cabinet for complete 30m full gallon qrp rig.  Jim
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