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38-12 Volume control that will not stop audio - Printable Version

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38-12 Volume control that will not stop audio - Flint Hill Bill - 02-03-2014

I am restoring a 38-12 and have it playing after cap replacement and rewinding the secondary Oscillator coil. The issue is that with the volume control turned all the way down, I still have audio at the speaker. The control does vary the volume but just will not silence the radio when turned all the way down. Any ideas are appreciated.

Thanks,
Bill

RE: 38-12 Volume control that will not stop audio - tab10672 - 02-03-2014

Have you sprayed it out with contact cleaner?

RE: 38-12 Volume control that will not stop audio - morzh - 02-03-2014

Have you simply measured your volume pot and made sure it is what it says and that the wiper connects to the lower pin when the volume is all the way down (should be within 50 Ohm or so).

How loud is it when turned down?

Simple test - short the wiper and the lower pin, and see if this brings the volume down the way it is expected.

RE: 38-12 Volume control that will not stop audio - Flint Hill Bill - 02-03-2014

Sorry, I forgot to mention that I changed out the pot with a 500K as the schematic called for. I double checked to be sure that the wiring is OK. I checked the resistance and that may be the issue. I have 1.6 when the control is in the off position and just off of off it reads 27K. That may be a bit much??? Maybe this pot is bad. I had to attach the on/off switch to the pot when it arrived, but it seems like there is only one what to put it together.

RE: 38-12 Volume control that will not stop audio - morzh - 02-03-2014

Cleaning it (might have to open unless it has that hole in the case) and Deoxit might do the trick.
When the wiper is in an extreme position it should have a low (below 100 Ohm) resistance to the respective end terminal.

RE: 38-12 Volume control that will not stop audio - gregb - 02-03-2014

Flint Hill Bill:
I have run into the same problem with some of the new pots out there. Seems a person has to hand select each one as they are not all the same. I had a 500K that all the way down but not into the off switch it still read 34k ohms and I had the same problem with the audio still on enough that it was a concern.

Gregb

RE: 38-12 Volume control that will not stop audio - Flint Hill Bill - 02-04-2014

Thanks Gregb, I will have to look around for a better quality pot, if they exsist.

And thanks to all who offered comments.

Regards,

Bill

RE: 38-12 Volume control that will not stop audio - morzh - 02-04-2014

Don't necessarily look for the new pot, just clean the existing one, it might be as good as you need it, just dirty. We typically do not discard dirty pots, we clean them.

RE: 38-12 Volume control that will not stop audio - tom.seeger - 02-05-2014

The new pot should be an audio taper pot not linear. A linear pot may have too much resistance at minimum setting.
However if it is a linear taper pot, you can try adding a 50K-100K ohm resistor between the wiper and low side of the pot. This will have the effect of unlinearizing the volume control similar to an audio taper pot. The down side is you will lose a bit of volume at the max end.