CRT clock question

[Morris Odell]

Hi all,

A few years ago I picked up a 1970s vintage Sperry Mk-8 Radar indicator unit
with the intention of making a scope clock. It's finally getting some bench
time and before starting on a long and painful reverse engineering effort I
was wondering whether anyone might have some data or schematics about it. It
will be an interesting challenge - I've never done anything with a
magnetically deflected CRT before.

Thanks in advance,

Morris

[Ulysses Balis]

Looks like there's a manual for sale on ebay right now, complete with schematics.  You're in luck.

http://www.ebay.com/itm/Sperry-Corp-MK-8-Radar-Service-Manual-w-Schematics-44281-/300912947775?pt=LH_DefaultDomain_0&hash=item460fcf323f

-ub

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[greg...@hotmail.com]

Sometimes it's more bother to reverse-engineer than to start-over.

Have you been able to get a spot on the screen yet ? You want to make sure the intensity is very low, and unfocused. Once you've got that you might try experimenting with the deflection yoke the see how much drive-current is needed. If you are lucky enough to have 2 audio generators, try driving the horizontal & vertical separately to produce lissajous patterns. We used to do that with TV sets years ago....

[John Rehwinkel]

Those are interesting. Many radar units have a fairly low frequency sweep, which can make it tricky to use them as scope clocks.

If you end up having to replace the deflection amplifiers, look at the schematics of vector monitors: the trick is to use op-amps
driving power transistors to switch plenty of voltage to the yokes, with current feedback from sense resistors. The op-amps will then
drive up the voltage to drag the current around through the inductance of the yokes. If the yokes won't behave, you'll either need
more voltage or new or rewound lower inductance yokes. Small ones (like the Vectrex) drove the yokes directly with power op-amps
like the LM379.

I'm working on a similar lashup myself, in order to use common magnetically-deflected CRTs. When I was a teenager, I'd
modify TVs like Greg mentioned, pulling the original yoke off the CRT (but leaving it in circuit, so the high voltage is available),
adding a second yoke and audio amplifier, and using them to display big lissajous figures. I made several of them for friends.
I had plans to try driving colour CRTs with bandpass filters for a "colour organ" effect, but never got around to it.

- John

[Oscilloclock]

Oh boy, I salivate every time I hear folks mention the possibility of re-purposing magnetic deflection CRTs. Good luck Morris and John!

Morris, would you be able to post a photo of your Sperry unit? I wasn't able to spot one readily on the web.

Aaron

[Morris Odell]

Thanks very much to everyone who replied! I have the manual coming which will help a lot in designing deflection amplifiers. At the moment the display is apart but as soon as I put it back together I'll post some pics. I'm really looking forward to the challenge of getting it working.

For my earlier radar clock I generated all the video with a micro but for this one I've been toying with the idea of doing the circular sweep with a synchro resolver driven by a stepper:-). It depends on how much room is available in the indicator once I remove all the radar stuff.

More news as it breaks!

Morris