Nifty thrifty antiquy score! 1956 DeVry Student Built CRO - diyAudio
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Old 22nd October 2013, 01:17 AM   #1
kbeist is offline kbeist  United States
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Cool Nifty thrifty antiquy score! 1956 DeVry Student Built CRO

Over the weekend I was given an antique all tube CRO for free!!! Yeah, free, oh and yes it works!!!! (albeit in dire need of re-capping as well as re-potting the pots). As soon as I got home I thought, "Ok this might be a boat anchor or a decent workable conversation piece." The case is not horribly damaged except for a few scratches. So I figgured I better open it up for a brush over look then lets see what kind of HV sparks with a display of antique paper confetti I can get? Plug it in and after a few loud crackling/sparking noises then quiet, the tubes began to glow!!! It took about 1-2 minutes to warmup. Viola! A green Liazous oval appeard on screen!!!! After fiddling with the knobs, I was able to elongate the patern horizontaly with a bit of touchy focus. Upon turning off, it done the loud crackle/sparking noise (bad power sw/intensity pot). I have obtained the schematics. I have 2 questions for anyone reading this is:

1: Is this worth recapping for use as a low freq scope? Or just a heap of antique?

2: If so. I did not recieve any student built probes so.... DIY probe will be built. The vertical/Horizontal input of the scope has series connected .25uF cap each prior to the 1M div pot. The external triger input has a series connected .1uF cap prior to the 500K pot. What kind of termination is that??? 50,75,100,300,600 or infinite Ohm?

As a side note I did find out on a Ham antique radio site that these were Devry kits sold to students as a requirement to be built by the student. They are a bit on the rarity for 2 reasons. 1) Devry did that from 1953-1957~9. 2) Most students did not put them in a fully enclosed case, making them prone to damage. Most if not all students upon graduating either purchased a better scope or worked somewhere with access to a better scope.

Last edited by kbeist; 22nd October 2013 at 01:32 AM. Reason: added info
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Old 22nd October 2013, 01:21 AM   #2
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I think you paid a fair price for it.....(!). You can get some really nice used O'scopes on eBay. Pay a little, and get a lot better scope....
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Old 22nd October 2013, 01:36 AM   #3
kbeist is offline kbeist  United States
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I will be getting a new Rygol package deal for ~800 (scope and analyzer) 2014 Tax time anyhow.

Last edited by kbeist; 22nd October 2013 at 01:38 AM. Reason: added
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Old 22nd October 2013, 01:57 AM   #4
sreten is offline sreten  United Kingdom
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Hi,

If anyone is wondering , CRO = cathode ray oscilloscope.

rgds, sreten.
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Old 22nd October 2013, 02:01 AM   #5
kbeist is offline kbeist  United States
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A CRO display is electricaly and mechanicaly different than a CRT display the only thing they truly have in common is the operational theory.
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Old 22nd October 2013, 03:29 AM   #6
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Well, yeah, as precision instruments go your unit was never much to brag about. I'd swag the basic (DC) voltage accuracy in the 5% to 10% range and the timebase accuracy not quite that good. The vertical frequency response is probably no better than 1 MHz; perhaps only a few hundred KHz.

As you have discovered it has historical significance as a good example of the "learn by building" philosophy used in most of the trade schools (especially the correspondence schools such as DeVry) from their inception in the 1930's up through the 1980's or so. Even though it is very limited as a measuring instrument it's still rather useful as a basic waveform monitor or approximate level indicator - e.g., watching for output waveform clipping while your "real" oscilloscope takes accurate measurements of more subtle characteristics.

To the general public, ANY 'scope using a CRT display has a definite "mad scientist's lab" aura about it. Put it in a room with any Nixie-tube instrument (freq counter or voltmeter) and a Jacob's ladder, and you have an almost complete set for a low-budget film. (If you're less than about 55 years old you need to look at the clip at http://www.youtube.com/watch?v=8CtjhWhw2I8 for inspiration.)

If I still had my gig as an instructor for DeVry Online, I'd love to have it sitting on the bench - and probably even use it a time or two - when I did real-time webcam demos of Lab exercises. Otherwise, I'd be tempted to leave it more-or-less permanently connected across an amplifier output channel to fascinate and amaze my casual visitors.

Dale
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Old 22nd October 2013, 09:26 PM   #7
kbeist is offline kbeist  United States
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Ah yes. I am under 55 but I do remember watching TOL as a kid around 74'-78'. Off topic my fav short was the one about the camera that took pictures of the near future. And when I was in electrical school we 12 students hooked up an inpressive jacobs Ladder with a nice oilbath transformer aquired from the defunct Goodrich plant in Miami, Ok. Taking 120V to 5KV, and #4 ground wire. Pretty cool lighting a cigarette. Just incase you wonder about our safety, that was why we did it. Learning that voltage potential can be leathal. I like your idea of a permanent hookup to an amp output.

Last edited by kbeist; 22nd October 2013 at 09:35 PM.
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