Tektronix 2225 Oscilloscope control knob

I bought my Tektronix 50 MHz scope used a few years back. It came missing the control knob for trigger level. I would frequently swap the "holdoff" knob, located directly below it, until one day, one of the two prongs seating the knob into the scope finally snapped off due to fatigue and frequent insertions. Typically, I'm only using one channel on the scope, so I was very carefully using the channel 2 position knob in place of the two knobs I was short.

When I knew I was getting a 3D printer for Christmas, this knob was actually the first thing I modeled. I modeled it first with a 1mm split in the tip, much like the original. This worked for a short time, but of course PLA is even more brittle than the original plastic used in the factory knob. I modified my model twice, first with a .5mm split, which prints a little stringy, and still likely to fail, and again without a split at all.

I've been using the scope with the non-split knob for the past few weeks. It's solid and less prone to failure, maybe even more so than the original.

This knob is intentionally a snug fit into the trimmer, however I don't advise forcing it too hard, risking damage to your vintage scope. It should only take a few seconds to sand or file the tip for easy insertion if the fit is too snug.

This knob may be used in place of either channels position knob, the trace step knob, the horizontal coarse and fine positions, trigger level, and holdoff.

Since I was missing two knobs, I actually opted to print the knob in both yellow and blue. I use the two colored knobs, yellow for vertical position channel one, and blue, vertical position channel 2, and marked my probes in the same colors.

As I stated, my original design and intent was to duplicate the factory knob as closely as possible, which I did initially, but I REALLY don't like the split tip knob for durability. I'm including the split knob STL, but I would urge you to use the non-split version I've included.

I printed these at standard .2 resolution on my CR-10 knock-off printer, using mostly the default Cura CR-10 profile, which I believe uses 20% infill. To avoid a friction causing seam in the center portion of the knob, I did configure "Z Seam Alignment" to "random", and that works quite well for me.

Hopefully somebody will find this useful.

Category: Electronics