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  #1  
Old 05-20-2018, 08:26 PM
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Zsuttle Zsuttle is offline
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National CRO Oscilliscope

So I stumbled across this Early scope (If you call it a scope) in an antique store, any information on it? I've seen bare bones minimum from my searches, namely a few photos and limited info.
It's kinda cool though, not really much practical use, but it would be cool to see it working again.
No labels on any of the knobs either, I figure a manual must be in existence somewhere.

Datatag says
NATIONAL
Model: CRO Number: E
Cycles: 50~60 Volts:105-120
National Company INC.
Malden, Mass. U.S.A.
Thanks all,
Zach
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Old 05-21-2018, 01:17 AM
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http://www.myvintagetv.com/vintage_test_equipment.htm
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  #3  
Old 05-21-2018, 12:05 PM
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Looks like a simple ham modulation monitor, likely for displaying trapezoid patterns when connected to an AM transmitter. I suspect that it is very similar to this smaller CRM model:

http://www.oscilloscopemuseum.com/os...-crm-sxxx.html

http://www.oscilloscopemuseum.com/up..._schematic.jpg

jr
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Old 05-21-2018, 03:21 PM
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Well, some of the values on the resistors differ, but they're known values. Any idea for a range for the filter caps?
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Old 05-25-2018, 11:23 PM
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The 2 inch model (CRU) isn't much different in design from the 1 inch CRM:

https://stevenjohnson.com/oscillosco...tional-cru.pdf

But i'm guessing that the 3 inch model might use somewhat higher voltage. The max for the 3 inch CRT is specified as 1500 Volts, so C2 might have to be rated at a higher voltage.

jr
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Old 05-26-2018, 06:50 PM
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Quote:
Originally Posted by Zsuttle View Post
Well, some of the values on the resistors differ, but they're known values. Any idea for a range for the filter caps?
There is only one filter cap, it's 1uF @ 1000V

Chuck
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Old 05-26-2018, 10:32 PM
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Then, anyone have any advice on where to get this type of a capacitor? I've yet to see an electrolytic with such little capacitance but such a high voltage. I've seen quite a few of the film style though, and at reasonable prices. Would using one of there in series with a diode (say a 4007) work as a substitute? I'm not very well versed with caps, but something tells me that this wouldn't work (Though doesn't stop me from asking)
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Old 05-27-2018, 12:21 AM
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They're not electrolytic.

Is it bad ? I can't remember what is actually in it, but usually they are oil filled cans and rarely are bad.

If it is bad you can use a couple of 2uf @600v units in series.

Chuck
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Old 05-27-2018, 09:17 AM
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Quote:
Originally Posted by ChuckA View Post
They're not electrolytic.

Is it bad ? I can't remember what is actually in it, but usually they are oil filled cans and rarely are bad.

If it is bad you can use a couple of 2uf @600v units in series.

Chuck
I wish it was oil filled, It tested leaky and I decided to restuff the enormous container. It's a pretty standard metal housing, paper innards, tar filled, pain in the rear, cap.
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