I’ve recently had to debug several scope’s 2kV-3kV HV supply and the CRT’s Z-axis waveforms at 2.5kV. So far I’ve got away with using a homemade 1000:1 voltage divider and a multimeter. Since that is crude and not particularly safe, I’m not going to mention the details in order to avoid someone apeing me and hurting themselves.
Then, at a recent auction I managed to pick up:
- a 40kV meter for measuring 17kV anode voltages, but which barely registers 2kV
- a Tek P6013A 12kV 1000:1 100kHz scope probe
The probe was functional but missing part of the handle. While not strictly necessary, I wanted to have a little fun fabricating the missing part…
I asked various people at my local Hackspace how they would make a handle, but all the suggested techniques for the large thread seemed tricky and would require buying equipment. Richard Sewell kindly offered the use of his thread gauge to measure the thread, and I eventually decided the easiest, surest, cheapest and fastest way was to 3D print a handle.
Not being sure I would be able to specify the thread sufficiently accurately, I decided to add a lip to the original design, so if the thread was loose I could still jam the body against the lip. It took me a half a day to create the model using OpenSCAD, most of that being taken up with triple checking all the dimensions. The Hackspace’s RepRap 3D printer was inadequate for making the thread, but from previous experience I knew that both Shapeway’s “strong and flexible” nylon and Dangerous Prototype’s SLA materials would work well. The SLA was cheaper (£13 delivered), so I chose that.
In the event the handle fitted perfectly, better than I had hoped.
So with a small amount of money, half a day’s work (plus some thinking time), and a little help from my friends, I can now debug CRTs less dangerously – and when I give up restoring scopes, I can eventually sell a working probe for a relatively obscene amount of money.