[davemc]

Looks like I may have tone control trouble! When I first did my survey, the tone control pot was questionable. But at that time there were leaky capacitors and some shunting resistors that would affect a clean measurement. After disconnecting the control, I was able to get a good measurement. The control (part number 33-5508-2) was supposed to be 6megs. The control measured about 16megs across the resistance element (rather than 6 megs). But the action is really weird. If I measure from the wiper to one end of the pot, the resistance starts near zero and goes up to about 16megs at approximately ½ rotation. The resistance then stays at 16 meg for the remainder of rotation.  Measuring from the wiper to the other end, the resistance starts at 16megs and stays there for about ½ rotation.  It then smoothly moves down to near zero ohms! It almost appears that the resistance element is split at about the middle. Each end starts at near zero, increases to about 16megs at ½ rotation, and then does not change for the remainder of the rotation. I don’t know how they did this – it looks like a normal control inside, although there are two rotating contacts that move together on the resistance element. I have included a portion of the schematic that includes the tone control. It appears that starting from one end, as the control is rotated the bass is gradually increased or decreased. As rotation continues, treble is cut.

[Image: http://i261.photobucket.com/albums/ii80/...ontrol.jpg]
 
The control may work as is, but certainly does not match the schematic as far as value. I did clean it, but that did not change anything. I’m not sure how this control could be replaced with other than a 5 meg normal control. The original appears to be tapered on BOTH ENDS! Does anyone happen to know for sure how this circuit works?  Any suggestions as to a replacement if needed?