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Re: Where did all the parts go?
Clive"Max"Maxfield   2/14/2014 8:52:55 AM
@Caleb: yep, beautiful tubes!

I know it's not the size of your tubes, but what you do with them that counts ... but dod you see the video of my outrageously bodacious tubes?


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Antique scopes...
Jean-Luc.Suchail   2/14/2014 2:36:16 AM
I syill have my old Tektronix double bean oscilloscope from 1958 (actually older than myself), still in good shape, fully operational (I just had to change a 6AN8 tube from the timebase).

This oscilloscope has a true differential input with 100microvolt per division sensitivity, I have never found this on new digital scopes. And last but not least, it does not take 10 minutes every time you use it to remember how to set it and finally get a trace on the display.

Caleb Kraft
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Re: Where did all the parts go?
Caleb Kraft   2/13/2014 9:03:44 PM
yep, beautiful tubes!

Caleb Kraft
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Re: The plastic (with the grid on it) came from EICO with the scope.
Caleb Kraft   2/13/2014 9:03:14 PM
interesting! I assumed it was a home made addition due to how roughly cut the plastic disk was!

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Re: Found at MIT
sreaves22645   2/13/2014 8:44:15 PM
That is a newer one that could have been manufactured as late as the 1980's. I have one and use it and the HP 200CD all the time. I also have a late 30's or maybe early 40's HP200B that still works!

Enjoy the generator it is still a very good one!





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Re: Deflection
salbayeng   2/13/2014 7:05:00 PM
IIRC the long neck is required to get a good quality image, 

A long electron gun is required to get a sharp colinear electron beam before it gets to the deflection plates. (otherwise you get out of focus spots, or oval spots that change with position)

The other reason for the length is to deflect the beam gently to improve linearity, deflection angle is proportional to deflection voltage, while the x position (on a flat screen)  is  tangent(angle) . If you use normal radio tubes , you only have ~ 100v of usable deflection voltage compared to say 1000v of acceleration voltage so you are limited to 1:10 deflection anyway, The other effect is that a fully deflected beam (at 100v) sees only 900v of acceleration, compared to 1000v on centreline

Shorter tubes have been made where linearity is not that critical.

see: http://www.crtsite.com/oscilloscope%20crt.html

PS the first "Oscilloscopes" were made ~ 120 years ago, i.e. they predate vacuum tube triodes by three decades,  There are some nice photos here: 


PPS variants of CRT's were used as memory elements in the earlier valve computers.


R Sweeney
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Re: Fire hazard
R Sweeney   2/13/2014 6:27:37 PM
The MOST dangerous thing about these old devices is the lack of a grounded chassis and three prong grounded line cord.

I have seen Heathkits with a fused NEUTRAL, which would allow a shorted power supply to blow the neutral, then pass full current 120v to the metal chassis. Most pre-war radios lack isolation transformers, which added cost.

But, you can add a safety grounded cord, and the rewards (even the smell) of restoring these old devices are rich.

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The plastic (with the grid on it) came from EICO with the scope.
kartys   2/13/2014 6:15:02 PM
Caleb said "An interesting feature you can see is that there is a grid on the display. This model did not come with a grid on the display; someone actually added it after the fact. You can see the original without the grid here. The grid is a piece of overhead transparency with a circle of acrylic cut to fit in the rim. It is held in only by friction on the felt ring."  But Caleb is wrong:  I built an EICO model 425 from a kit in the late 1950s, and it came with the round plastic with the grid on it.  No one "actually added it after the fact."   I still have both the round plastic and the scope, which still worked the last time I turned it on (over ten years ago).  The vertical and horizontal amplifiers have potentiometers to adjust their gains, so they are not calibrated.  Although there is no triggered sweep, it was still possible to fiddle with the controls to maintain a steady trace.  But I never enjoyed using this scope any more after I started using Tektronix scopes in the mid-1960s.     

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Fire hazard
salbayeng   2/13/2014 6:07:50 PM

w.r.t. "I'm pretty sure that this type of power light would be considered a fire hazard by today's manufacturing standards

Actually, its probably the safest part of the scope, the bulb runs off the 6.3v filament winding. 

On the other hand,  the rest of the exposed wiring will have hundreds of volts on it while running.

You really need to take heed of the advice offered, regarding conditioning electrolytics before powering up these old valve powered sets.

Have fun with it anyway! Its probably only useful for Lissajous figures, or maybe with a microphone, or sonar,  these old scopes aren't much use for troubleshooting modern electronics, as they are AC coupled, non calibrated, and have almost non existant trigger capabilities, with non linear timebases.



David Ashton
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Re: Old Scopes
David Ashton   2/13/2014 5:52:47 PM
@Bill - further to Lissajous figures - many years ago Elektor magazine did an article entitled "Spirographics" - using a scope to make patterns like the old "Spirograph" drawing set which really just made complex lissajous figures. I had a Spirograph when I was a kid.   I still have it somewhere (the article), maybe one day I'll get around to making one.......

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