Some details about an unusual project. I am thinking there might be some magnetics gurus here who could find it interesting. Can anyone speak to the characteristics of electromagnetic deflection X-Y displays?
The summary is that I would like to use a 'sparkfun' or equivalent oscilloscope clock with a 10" round CRT. Rather than consume P4 TV tubes, I have a few radar CRTs that will do. Using a scope for the scopeclock is not good for the scope and the display is too small from across the room.
The old original "
cathode corner" scope clock has far better, sine-generated, numerals, but it is out of production and the person in authority has not replied, probably busy. I sincerely hope he will release a new version because of the superior characters generated by his scope clock board. The sparkfun board is OK, but it draws points, not the cleaner looking lines.
The H and V signals (XY) from the sparkfun clock are much too fast for magnetic deflection CRT yokes commonly found in TV sets. There is a DAC write each 2.25us, but a custom firmware has enabled a 100-150us delay for each plotted point.
Even so it is too fast for a common display having a 20KHz response. Calculations showed that with a regular TV yoke, the amplifier voltage must exceed +/-300V and the amplifier must supply up to 3 amperes.
Therefore a yoke must be rewound using less turns of thicker wire so the inductance will be very low, and a simple lower voltage amp can be used. This is borne out from inspecting an old military XY display. Its yoke has only a few turns of quite heavy wire, and tiny inductance. The power supply for that unit was about +/-40V at 10A
Attached are some pics of what has been done so far with an unmodified Wavetek electromagnetic deflection scope. I also have a H/P electrostatic deflection scope, model 1300 but it is not working. I need the books on both if anyone has them.
I have not yet rewound a yoke to enable a suitable amplifier to be built and used. I previously estimated a 60KHz bandwidth to be adequate but now believe a 100KHz bandwidth is possible and reasonable with the right yoke winding.
There is a very good read on crts, deflection amps, and design of yokes here. It is tube-type stuff, but the ideas are what matters.
http://bunkerofdoom.com/lit/mitser/V22.PDF
Download this, it's 'large'.