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Antique Electronics Autopsy: 1950s Eico Oscilloscope Model 425

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R Sweeney
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Re: Old Scopes
R Sweeney   2/13/2014 5:42:36 PM
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Some of the wonderful things about the amateur radio community is that it is seamless, universally friendly, helpful, and well equiped.

There is a HUGE following of vintage tubed gear and the folks with the knowledge and tools to restore gear are EVERYWHERE, willing to help with access to a vintage tube tester (no longer found in every drugstore) and autotransformers. And scopes and signal generators for that matter.

Find your local amateur radio club, attend a meeting, request help on a tubed project and it will be answered.

MeasurementBlues
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Re: Old Scopes
MeasurementBlues   2/13/2014 5:36:37 PM
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If you watn to see lots of old scopes, lots of them, then visit EDN T&M DesignCenter tomorrow. We have a history of scopes from Vilnius.

http://www.edn.com/design/test-and-measurement

 

David Ashton
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Re: Old Scopes
David Ashton   2/13/2014 5:11:44 PM
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@R Sweeney - Excellent advice, and when I said it probably still works I should have added the caveat about the electrolytics.  Written in haste.....

Very few people have a variac or a tube tester to hand.  A test of the disconnected electrolytics with a lab PSU at maybe 50V is a good start.  If you're in the US you could then use an isolation transformer (a must) and a rectifier with a  beefy 10K resistor in series to put about 160V on them, Leave it on for a bit , monitoring the current (should go quickly to a few mA or less), to let them reform.  But caps of that age will usually be dry (= low cap) if nothing else.

If you can just replace the electrolytics (which is probably the best way to go) then you'd probably be fairly safe in trying a switch on, with a meter across the main electrolytics - if the voltage does not go up to a few hundred volts right away then switch off and dig further.

Bill_Jaffa
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Re: Old Scopes
Bill_Jaffa   2/13/2014 4:44:07 PM
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OMG, nice to see Lissajous figures cited, also see: http://edn.com/electronics-blogs/power-points/4418467/Time-tested-technical-tools-and-techniques

DarkMatter0
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Re: Old Scopes
DarkMatter0   2/13/2014 2:50:53 PM
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Sage advice! I cringed as soon as I saw the photo with the caption "Power on".  Caps are easy to replace, but a burned out winding in the power transformer is usually fatal.

R Sweeney
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Re: Old Scopes
R Sweeney   2/13/2014 1:45:39 PM
As a rebuilder of old tubed Heathkit ham gear, you NEVER just turn on the power and see what happens.

The 60 yr old paper caps on these pieces are almost 100% quaranteed bad, open or shorted. And those bad caps can damage irreplaceable components on failure, like hard to find transformers. And a surprising number of carbon resistors crack with age.

So,

Step 0: get and read the manuals

step 1: replace the paper caps with modern high quality (non-Chinese) electrolytics

step 2: clean all the switches, pots, sockets

step 3: test the tubes

step 4: use a variac to SLOWLY bring up the line voltage to avoid in-rush issues with components which have not seen a magnetic or electric field for half a century.

step 5: if it works, rejoice, if not troubleshoot and find the dead guy(s).

step 6: Enjoy the rebirth of someone's old friend.

Max The Magnificent
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Where did all the parts go?
Max The Magnificent   2/13/2014 12:43:09 PM
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@Caleb: The surprising thing to me was when you took the cover off -- seeing how few components were used -- I was expecting it to be jam-packed with circuit boards and transistors -- I hadn;t realized it was vacuum-tube-based.

Dale Shpak
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Deflection
Dale Shpak   2/13/2014 12:13:28 PM
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I am also circa late 50's and used this scope when I was a kid.  For the younger crowd, an interesting aspect is the long neck of the CRT which is because scopes used electrostatic deflection rather than electromagnetic deflection.  Faster, but a narrower deflection angle.

MeasurementBlues
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Re: Found at MIT
MeasurementBlues   2/13/2014 11:10:06 AM
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Also found this HP 201-C Audio oscillator. Many more photos where these came from.



MeasurementBlues
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Found at MIT
MeasurementBlues   2/13/2014 11:05:45 AM
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I photographed this one last year at the MIT Electronics flea market. I'll go back this year, assuming winter ever ends.



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