Recently [Roberto Barrios] got his hands on a Rohde & Schwarz EB200 monitoring and surveillance receiver that, despite its late 90s vintage, was in mint condition. Aside from damage to the main dial, that is, which was very much broken. With no off-the-shelf replacement available in 2023, the obvious answer was to get a close-enough dial knob with the rough proportions and use a lathe to machine it into shape. Initially, [Roberto] had used some filler material to replace the front of the original knob that was missing, but this was a decidedly inferior tactile experience with questionable long-term reliability.
The challenge in replacing the original knob with a proper replacement was in how the dial knob is mounted on the receiver, as an internally threaded shell that goes on the internal dial encoder assembly. With a lathe at his behest, taking an off-the-shelf dial knob that accepts a 6 mm shaft and turning it into a compatible knob was a straightforward affair. Removing the excess material and creating the internal 1 mm pitch thread allowed the newly made knob to fit on the receiver like an OEM part. The only niggle was having to remove 1.8 mm off the face of the brass body to get the knob to sit close to the front panel.
Unlike the old patched-up knob, this new one is fully out of metal and has the absolutely essential feature of the recessed area for easy fine-tuning. Although perhaps not the most exciting fix for old gear, it’s decidedly essential to keep it functional.
Wow! Nice catch. That receiver is certainly worth the effort you put into building a new knob!
Happy listening!
The recess is not for fine-tuning; it’s for speed. The large diameter of the knob is for fine tuning.
The recess is for speed; the large diameter is for fine tuning.
Great job of reverse engineering. I probably would have tried to do a 3D print first. Wouldn’t have looked as nice but probably a lot quicker to make.
When you have a machine shop at your disposal, it’s often fun to hunt for things to do to show it off. Can’t say I blame ’em
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