Prof. Tweed Shake-down questions.

[dpresley58]

I'm trying to wrap up a Prof Tweed and ran across some problems. The schematic is at http://www.runoffgroove.com/professor.html. Sorry to bother you guys with newbie questions, but I've looked at the troubleshooting guides and can't figure it out.

The question arose when I was setting the voltage at the three trim pots. All the transistors are socketed MPF102's which were oriented according to the data sheet.

The 1st and 3rd pot trim out just fine, and the pin voltages at the drain and source fall pretty much in line with whats posted for a baseline. The second pot is erratic and seems to drain after setting. For instance, after I adjust it to 4.5v, the needle will slowly fall. Also, the pin voltage is much higher at the source than the ones posted. Instead of a little over 1v, I'm getting about 3.5.

There's also what can be called a "proximity effect" when I'm trying to adjust it. When I remove my hand after an adjustment of the pot, the voltage goes back up. I can move my hand near to and away from the board and watch the needle move. (All the offboard wiring has been installed, but not connected, if that makes a difference. I've taped off the ends for identification)

I initially thought I had a bad pot, so that was checked. I've carefully looked downstream to make sure of component values and placement. The transistor has been changed out with another I have to see if I just had a bad one in the socket... They both had the same problem.

Any ideas on this? And is there any reason these three legs are using pots instead of resistors to step the voltage down? (Again, I qualify my newbie status in case that was a ridiculous question...)