Elektrishun
Ultra Member
Replacing a potentiometer for a volume control on a piece of audio equipment. The original is a vintage CTS potentiometer. Accorrding to what I have been reading online vintage CTS means "quality". During some tests it seemed to be suspect. Unfortunately I had no choice but to be destructive when removing it (what if I am wrong, oh well). I believe the previous owner of the audio equipment glued all the plastic knobs onto all the pots which have plastic shafts. So I had to drill out the plastic shaft from the back to free the device from the panel. To salvage the original knob took even more work as to carefully drill out the remaining nylon(?) as close to the wall of the knob as possible. Then further remove micro amounts with a Dremel tool. Lastly, scratch out the last bits with a modified micro file that has been ground down to a "sewing needle" tip. But the knob survived!
Now, I have a replacement potentiometer which meets all the important specs. Plus it was readily available and cheap. But it might be temporary for testing only because it is not considered a quality potentiometer. Then again it might work just fine. So I have decided to at least try to install it in such a manner that if it solves the problem it can be a permanent rather temporary installation.
That's where the M7 x 0.75mm tap comes in.
Turns out the old threaded portion of the original CTS pot slides over the shaft of the dimensionally smaller replacement up to it's threads. The old CTS threaded portion is thick enough that I believe I can tap the necessary threads to screw the new pot into the old. This will give a solid mount in the original opening in an almost identical fashion as the old pot.
Surprised not to be able to find this size of tap listed at McMaster-Carr or Grainger. But Amazoon has it. For a few extra yen I decided to get the matching die; M7 x 0.75mm Tap and Die
Pictured below is parts of the old pot (including the original large spacer) and the new pot beside it, plus a rough idea of how it will go together (alignment pin on new potentiometer will be removed):
Tap should arrive on Saturday.
Now, I have a replacement potentiometer which meets all the important specs. Plus it was readily available and cheap. But it might be temporary for testing only because it is not considered a quality potentiometer. Then again it might work just fine. So I have decided to at least try to install it in such a manner that if it solves the problem it can be a permanent rather temporary installation.
That's where the M7 x 0.75mm tap comes in.
Turns out the old threaded portion of the original CTS pot slides over the shaft of the dimensionally smaller replacement up to it's threads. The old CTS threaded portion is thick enough that I believe I can tap the necessary threads to screw the new pot into the old. This will give a solid mount in the original opening in an almost identical fashion as the old pot.
Surprised not to be able to find this size of tap listed at McMaster-Carr or Grainger. But Amazoon has it. For a few extra yen I decided to get the matching die; M7 x 0.75mm Tap and Die
Pictured below is parts of the old pot (including the original large spacer) and the new pot beside it, plus a rough idea of how it will go together (alignment pin on new potentiometer will be removed):
Tap should arrive on Saturday.