Cautionary note here. MANY older oscilloscopes generated their CRT
voltages directly from the A.C. mains connected transformer. ""NOT"" low
current. I just finished restoring a Heathkit oscilloscope from not that
long ago, where this was implemented.
Ira.
On 10/28/2025 3:07 AM, TomJ wrote:
On Mon, Oct 27, 2025 at 4:31 PM Mac Doktor <[email protected]> wrote:
Note that over at the GeigerCounters group talking about building
negative HV power supplies can get you banned. A couple of people
found that out the hard way after having been warned. The -900V
supplies in Geiger counters are grandfathered in, of course, and
the currents are very low.
Certainly, the voltages involved are no joke and can be lethal. CRT
voltages typically are very low current as well, but I suspect still
very dangerous. Though it seems a bit
nanny-state' to ban legitimate scientific discussions - you can just
as easily discover mortality working on your car or a home appliance.
In any event, I also received a very informative email from the
gentleman at Sgitheach... My understanding is that the crt tube
doesn't really care - it comes down how you want to design your
circuit. Having the high potential at the cathode makes the
deflection circuit easier to implement because the voltages are
lower. BUT, if you desire to incorporate some kind of intensity
modulation or Z axis, you now have to manage that end with high
voltages. The end result from a performance perspective will be the
same.
Thanks for the insight!
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