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RFT service-oszillograf EO 1/71 vintage oscilloscope

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I have one, with probes, manual and 'garantieurkunde' (for the warranty) and the 2MHz scope still works if you turn it on. The only date i can find is on the 'garantieurkunde', and it's from may 1964 i think. (i'm 18 years old).

I bought it from a friend a couple of months ago almost for free. (cost mee two local beers).

The only problem is, that i don't know how to control it. It's very different than the digital tektronix 1001 scopes we use at school...

I will post a better picture tomorrow.

A nice piece for your museum but hardly useable today, maybe for some very basic audio work.
But do post pictures, I have a similar West German unit from about the same time, the Hameg 107. Equally useless but nice to look at  ;D.

Scopes of this kind do not have a trigger control as you're used to, it probably hasn't even got a proper input attenuator.
One thing it doesn't have either is a calibrated horizontal horizontal deflection circuit, it's a free running triangular generator that generates the deflection. There should be a "Sync" or similarly labeled knob - that is basically the equivalent to the trigger control on more modern scopes.
So there's neither a way of judging the magnitude of the applied signal, nor it's frequency.

I do have a book on how to use these scopes somwhere, might dig that out to have a look through.


--- Quote from: einstein on July 25, 2013, 10:22:18 pm ---It's very different than the digital tektronix 1001 scopes we use at school...
--- End quote ---

Missing the Autoset button, eh?  :-DD

A bit of guessing from the picture in the link. Upper part is basic adjustments like intensity (upper left), and beam center (upper right)

Lower left side is the vertical (Y) control, and signal input. And it seems to have an input attenuator switch and fine adjust.

Lower right side seems to be the horizontal (X) deflection - see the small ramp figure in front of the word "Frequ.". That should be to control the frequency of the horizontal deflection signal.  Knowing that t = 1/f should tell you this is the timebase. Fine control above.  Ramp signal output seems to be in the lower right (again, they use the small ramp figure near the socket). So you could use that to drive some external instrument like a sweep generator in sync with the X deflection.

And there seems to be a sync adjust in the middle/center. That is for aligning the start of the horizontal deflection ramp with the signal - the closest you get to a trigger.

Lower middle seems to be input for external horizontal (X) deflection with an input attenuator. So that oscilloscope has an XY mode.

To the right between the external horizontal input and the internal horizontal output signal seems to be an intensity input. Today known as Z input.

A museum piece, East German design from 1956 if I understand the information in the link correctly. The price of two beer is OK for it. Get an audio generator and have some fun with it. Draw some Lissajous figures. Get an "octopus", draw some diode curve. Then polish it and find a place to display it in your lab, where it doesn't get in the way. 

When i bought it, i took it apart, to clean it and i found the pictures of that 'teardown'.

On the upper half, there's the on/off switch, and controls for the intensity of the display. But i'm in trouble with the knobs on the lower half...

For me, i want to check if a signal is actually a square wave, or check if the duty cycle changes when i turn the pot. I don't have that special electronics. Most things i design go only to about 1kHz. So 2 Mhz is more than enough.

Before you do anything else, I'd suggest you replace any paper/wax capacitors. Electrolytic caps of that age are also very suspect.

Vacuum tube gear of that era very frequently use capacitors with paper/wax insulation. The catch is that this insulation breaks down over time when subjected to air, and the cap becomes leaky. Mostly never a solid short, but they will leak DC current when subjected to the high voltage in tube gear.

The problem is that these caps were frequently used to block DC voltages between gain stages. Tubes, on their part, are generally like glowing JFETs, they want their control grid (gate) run negatively with respect to the cathode (source). Worse still, the grid circuit is mostly very high impedance. So when a small DC current leaks through a cap, it very frequently causes the next tube grid to go positive, causing the tube to draw way excessive power.

Unfortunately you frequently won't notice anything is amiss, until it is too late and a tube or an output transformer (in audio amps) die. Tubes can be abused pretty brutally, at lest briefly, but they are not indestructible. If their anodes visibly glow, then it is already way, way too late. Even if they don't, then you might still have a problem.

The rule of thumb with tube gear from before 1965-70 or so, depending on origin, is: It absolutely *never* just works, you *always* have to replace those blasted caps. Don't check, replace all those in critical positions at least. Yes, you can sometimes get the old radio/TV/oscilloscope/amp to 'play' just by plugging it in, at least for a short while. Yet bets are very good one or more tubes in there are quickly being fried out of their remaining useful life.

Never just plug in old tube gear as found, 'just to check if it works'. If you intend to sell it to collectors and other people in the know, say that it *hasn't* been plugged in, and provide detailed photos of the interior to show the condition of the circuitry. That is likely to bring higher prices for a rare piece of kit, as you are less likely to have ruined rare tubes or hard to replace transformers.

It is an *excellent* way of checking if someone like a seller of old tube gear on eBay knows what he is doing: If he has 'tested' it without further comment, then he is clueless. :scared:

Stop killing our remaining tubes, please. Old tubes are not semiconductors, don't plug the gear they are in before inspecting what is what.

PS: There are both brands and types of equipment, where this problem isn't too much of an issue. Yet even here there are exceptions, which means you *still* have to check before plugging it in.


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