I got this Kikusui 5091 used for US$ 50 bucks, as a reward for my pretty successful attempt to create a digital raster display from scratch on my oscilloscope, and finishing off my Game of Life in hardware that updates a 256 x 256 pixel field at real time 60 Hz frame rate (with the option of going up to 512 x 512). I find my oscilloscope screen too tiny.

But after buying that Kikusui 5091 scope I found out that it might be very different from a normal oscilloscope, as it's vertical frequency bandwidth is specified DC - 10 kHz only and especially its horizontal bandwidth is specified as only DC - 1 kHz. Only one kiloherz? That would limit the frame rate for 256 lines to only 4 frames per second! 4 Hz frame rate is bad.

So, why would that be so bad? What would be the point of such a scope?

Let me see if I understand this right on a high level:

  1. Real oscilloscopes use electric field deflection which allows for much higher bandwidth because you don't have that massive inductive impedance of the deflection yoke to counteract. You apply voltage and with resistance held low the deflection field generating "capacitor" is quickly charged and discharged and reverse charged. Not so with a coil where you must pull current changes with crazy voltages against massive momentary impedance.
  2. But the CRTs for real oscilloscopes need to be much longer for the screen size, so essentially if you want a larger screen, the mechanical trouble of a tube that might have to get a meter in length is just not worth it any more, so that's why they invented all these intricate complicated "fly back" circuitry, and added significant horizontal blank time to video standards such as NTSC to allow for the fly-back to occur.

Is that about right? And this means, if I want to have a prayer to use this Kikusui scope for anything like video, I would have to modify that horizontal deflection stuff, or maybe I would flip X and Y sawtooth and image coordinates such that I scan up and down lines that go right to left. Then at least I could get a 40 Hz frame rate at the 250 x 250 resolution.

Any other trick?

Might it at least be good for a vector screen? (Which is another thing I want to experiment with soon.)

  • 1
    \$\begingroup\$ Yes, that pretty much sums it up. The point is, the scope is perfectly adequate to the purpose for which it was designed. You're going "off label", which means that it's up to you to make sure it has the features and performance that you need. \$\endgroup\$
    – Dave Tweed
    Aug 2, 2020 at 13:52
  • 1
    \$\begingroup\$ $50 seems a lot for a crock of brown stuff. \$\endgroup\$
    – Andy aka
    Aug 2, 2020 at 13:54
  • \$\begingroup\$ Yes, unfortunately I am in a place where there is a dearth of decent stuff for decent price. \$\endgroup\$ Aug 2, 2020 at 15:50
  • \$\begingroup\$ Modern digital scopes use LCDs which don’t have much bandwidth at all. Maybe use it as a display - perhaps with an open-source digital oscilloscope innards. \$\endgroup\$ Aug 2, 2020 at 16:05
  • \$\begingroup\$ Realistically there is almost no point today, unless you really, really need the retro appearance. You could build some kind of digitizer which would re-synthesize things within the bandwidth of the CRT, but why? Once you've gone digital a nice modern LCD or OLED make so much more sense as a the display technology: lower power, safer, portable, replaceable... There was an era where DSO's put a synthetic image on a CRT (often with visibly distorted "dots"), but that era is long gone: having a real knobs on your scope is nice, but so is having the instrument only be four inches deep. \$\endgroup\$ Aug 2, 2020 at 17:34

2 Answers 2


You're in worse shape than you think.

It's true, you flip the image axes to take advantage of the higher bandwidth of the scope Y axis. You could then modify your raster scan so that one line goes up, then the next line goes down, then up, etc, in order to avoid the delays caused by the retrace time.

Your problem is the Z-axis modulation frequency, which is abysmal. It suggests that you can get a visible change in intensity in 10 usec. Problem is, a 256 x 256 raster will have 65,536 pixels, so you'll only get about 1.5 frames per second.

What this does very nicely is, indeed, a vector display. As long as you're not trying to display too many vectors per second.

If you go the vector route, be aware that for consistent trace brightness you'll need to manipulate your axis generator so that the spot velocity remains reasonably constant.


Alighment scope? sounds like what a tracking_generator paired with a Spectrum Analyzer would need, in aligning IF filters, or other filters


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