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Old 14th Dec 2012, 8:09 pm   #161
Refugee
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Default Re: Building an oscilloscope at home

It is looking good and reminds me of trying to make a scope out of an old TV set.
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Old 17th Dec 2012, 2:51 pm   #162
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Default Re: Building an oscilloscope at home

Here the small changes I did.

1.) I used -500V (instead of -600V) DC for the supressor grid circuit. This was the optimal value for max sweep length. Above this value it didn't oscillate.

2.) I used 47pF and 23.5pF for C11 (instead of 30pF). It worked fine with both values, but with 23.5 (two 47pF in series) the flyback sweep is more sharpen.

3.) I didn't used a potentiometer for RV47. Instead I used a resistive divider of the same value than the pot. I change the value ssevral times to simulate the movement of the pot, and I noticed no important changes in the trace length.

This weekend I got a sweep of 50uS. My most ambicious goal it to get a sweep of 10uS, but I'm very happy with my achievement till now.

****************************

There is a mistake on post No.159 . I wrote RV47 instead of RV44. The correct pot to change the sweep frequency is RV44.
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Old 17th Dec 2012, 8:55 pm   #163
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Default Re: Building an oscilloscope at home

Hi Miguel, some nice experimenting there; best to go for the sharpest flyback sweep.

If you want to go down to 10uS sweep do all you can to reduce stray capacitance and inductance.
This means the shortest possible leads and direct connections to valvebases without tag strips. Use a single earth (ground) point right at the valve.

Good luck and let us know when you succeed.

Ed
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Old 18th Dec 2012, 8:44 am   #164
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Default Re: Building an oscilloscope at home

One rule of thumb for scopes was that for a good sweep system, you needed about 20 harmonics of the sawtooth waveform in terms of bandwidth.

If you run your sweep to 10us (therefore 1us/division on the usual 10 divisions wide graticule) then the sawtooth was a 100kHz one, and you need about 2MHz of X amplifier bandwidth.

This figure is typical of HP and Tek scopes

Plenty of scopes have been built with lower bandwidth and work OK, but they show some non linearity, chiefly at the beginning and end of the sweep where the corners of the sawtooth get rounded.

Cheers
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Old 19th Dec 2012, 8:35 am   #165
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Default Re: Building an oscilloscope at home

I have come into this discussion rather late and haven't read it all. I built two oscilloscopes when I was a teenager. The first was based on an ex-army "Indicator Unit". There was a book called (I think) "The Oscilloscope Book", which described the conversion. It wasn't really a conversion as all that remained of the original unit was the chassis and VCR97 CRT, which required "only" 2000 volts.

The first lesson I learned was not to be tidy. Twisting the X and Y plate wires together looked neat but produced only a 45° trace!

As stated above, wires should be kept as short as possible. That means straight lines and a web of wires. I also discovered that some potentiometers don't like 2000 volts. The brightness pot. got quite bright!
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Old 3rd Jan 2013, 8:28 pm   #166
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Default Re: Building an oscilloscope at home

Hello everybody. I wish a Happy New Year for everyone.

I have done something on the scope project and I want to share with you.
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Old 3rd Jan 2013, 9:14 pm   #167
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Default Re: Building an oscilloscope at home

Very neat!

You *have* been busy!

David
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Old 3rd Jan 2013, 11:04 pm   #168
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Default Re: Building an oscilloscope at home

I am new to this list, and only saw this thread tonight. I have spent the last couple of hours reading through all the posts.
Miguel, you are a hero. As I read through, I spotted a few things, but they were all corrected in subsequent posts, and now you are nearly there!
We are lucky over here, one way or another we can get most stuff. I am into motorcycles amongst other things, and you can usually buy or make the stuff you need. However there are some people who buy a pile of old scrap, then spend thousands of pounds getting somebody else to "create" the old 'bike which they will then show, hoping to "win" the concours.
They would not last long in Cuba. You would be the one to get the rosette if I were judging.
One comment on your sawtooth waves. If you are going to have these driving the Xplates, surely you need some "holdoff" between each sweep. Without that, you are just varying the frequency and hoping to see your picture to see the picture, not triggering the deflection at the correct point. (Or am I missing something?)
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Old 4th Jan 2013, 2:31 pm   #169
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Thank you very much for your kind comments, gents!! I do my best.

Quote:
Originally Posted by MotorBikeLes
not triggering the deflection at the correct point. (Or am I missing something?)
I'm using the circuit used in the Serviscope Minor oscilloscope. The sweep is triggered by a flip-flop which is synchronized with the input signal. When there is no signal applied, it is in free-running mode, so I have the patterns showed in the pictures.

I tested it having a higher sweep frequency and applying around 20kHz signal directly to the flip-flop. I could see those holdoff section in the oscilogram. Then varying the input frequency, I could check that this holdoff time varies too following the input signal, so it was synchronized.

I will try to take a video of this, as I have not dismounted the circuit yet, to show the synchonization.
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Old 4th Jan 2013, 5:15 pm   #170
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Default Re: Building an oscilloscope at home

Hi Miguel,

Congratulations! on your efforts.

See in complete details with many photos, schematics & wiring diagrams a recent project of a simple oscilloscope using electron tubes:

It's in French, but Google translation should work.

Main site:
http://www.cfp-radio.com/

in the left column, scroll down to "Realisations"

then scroll to "Outils & Mesures"

and finally to:

"Un oscilloscope Simple"

Silly question: USSR CI-93 or 94 scopes sometimes turn up for cheap in France, they were quite popular "beginner scopes" in the late 1970s. If i buy one with a good CRT is it possible to Mail the CRT by itself to Cuba without getting stolen by your Customs/Post Office, etc.

Best Regards

jhalphen
Paris/France
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Old 4th Jan 2013, 8:21 pm   #171
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Thank you very much jhalphen. I'm reading that page right now. It could give me some ideas to improve my project.

Quote:
Originally Posted by jhalphen
Silly question:
The only silly question it's the one that is not asked.

Quote:
Originally Posted by jhalphen
USSR CI-93 or 94 scopes sometimes turn up for cheap in France, they were quite popular "beginner scopes" in the late 1970s.
I really don't think that C1-93 would be a beginner's scope. It is a very good dual trace scope capable to measure up to 50MHz, with many functions.
http://www.elektroda.pl/rtvforum/fil.../c1-93_443.jpg
C1-93

On the other hand, C1-94 is a beginners oscilloscope, designed with elementary controls.
http://www.mydarc.de/dk3wi/assets/images/C1_94_1.jpg
C1-94

As you can see they use diferent type of CRT.

Quote:
Originally Posted by jhalphen
If i buy one with a good CRT is it possible to Mail the CRT by itself to Cuba without getting stolen by your Customs/Post Office, etc.
I prefer you don't.
Possibly you could do that. Some chaps in this forum have sent me several component which I have use in this project, but CRT is another ball game.
CRT is bulky, fragile and possibly heavy due to the shock protection it needs inside a box. I guess it would not be stolen but if it exceed 3kg, it will cost me hard money to retrieve it from the post office.
On the other hand I have three of this CRT's, so I guess I will have spares for a while. Anyway, thank you very much for your offer.
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Old 4th Jan 2013, 9:22 pm   #172
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Default Re: Building an oscilloscope at home

Your waveforms. I had wondered if that might be the free running trigger, but (from memory) when I set up many TQ scopes with that arrangement, it was a small signal on the scope (100mV) and there was a sharp change in amplitude at the transitions from positive going to negative going. Very critical adjustment which would either not give the waveform, or go into high frequency oscillation if you turned the preset resistor too far one way or the other. I will be repairing a D67 shortly, and that has the same trigger method (solid state not valved though). Later TQ scopes (D63, DM63, D75 and D83) were quite different.
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Old 4th Jan 2013, 9:45 pm   #173
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Default Re: Building an oscilloscope at home

Hi Miguel,

Thanks! for the replies.

I now see the differences between C1/93 and C1/94. From re-reading page 1 of this thread, your scope with a dying CRT is the C1/94, correct?

Can you please give me the CRT model in this scope, i routinely scan European E-Bay for CRTs and East-block sellers abund with ex-USSR scope tubes.

3 Kilogram postal weight limit: the data sheet on the C194 might give the net weight without the parcel. The tube's length can also give an indication.

If you perhaps decide to build the scope described on the CFP-Radio site, the DG7-32 CRT is very short and lightweight. It was a popular tube and is quite easy to find. It was also used as the "DeLuxe" tuning indicator in some Marantz very high-end FM tuners.

Best Regards
Jerome Halphen
Paris/France
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Old 5th Jan 2013, 8:23 pm   #174
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Default Re: Building an oscilloscope at home

Hi Jerome, that sounds like an interesting use for CRT's, as tuning indicators; I must admit I had not heard of them, but a good use for small CRT's now that only Miguel is building scopes anymore.
Do you think the VCR97 (6") would look much more impressive than a 1CP1 (1")?

Do you have a copy of the schematic?

Best regards, Ed
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Old 5th Jan 2013, 9:08 pm   #175
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Default Re: Building an oscilloscope at home

20*log(6/1) = 15.56 dB more impressive, Ed.

Well, Mullard used a CRT indicator where everyone else used moving coil meters. And Mullard's CRTs seem to be less failure prone than Avo's meters... Hmmm

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Old 5th Jan 2013, 9:22 pm   #176
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Default Re: Building an oscilloscope at home

Hi Ed - & Happy New Year!

Use of CRTs as high-end tuning aids:

See Jean-Claude Jardine's description of how a CRT is used to orient a directional FM antenna to minimize multipath distortion. CRT photos at bottom of page.

http://tsf.pagesperso-orange.fr/mult...-multipath.htm

Other indication modes depending on the manufacturer's choices can also show signal strength as a vertical line whose length increases as the signal gets stronger.

Once tuned, the CRT could either be switched off or used to display Lissajou patterns of the audio stereo signal.

From memory, some tuners equipped with CRTs were the Marantz 10B, Marantz 150, Marantz 2110, Marantz ST-7, Stereo Receiver 4400, Day-Sequerra Model 1 (also had a panoramic display).

Dial in these references into Google to see photos of these vintage hi-fi products.

I have no schematics as these would be included in the service manuals of each products.

In my opinion, a VCR-97 would look monstrous & ugly, the electronics to run it would be much more voluminous than any FM tuner. However, you could use it as a panoramic display, i.e. a sort of simplified spectrum analyzer showing stations +/- a few MHz away from the radio's central tuning frequency.

Panoramic display adapters were popular with Ham-Radio operators. search here in the "Boat-Anchors" database for manuals & circuits. Heathkit made several models.

http://bama.edebris.com/manuals/

Best Regards

jhalphen
Paris/France
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Old 5th Jan 2013, 10:27 pm   #177
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Default Re: Building an oscilloscope at home

Thanks for that Jerome and a Happy New Year.
I have quite a few instrument CRT's here of various sizes that are looking for new applications.

Ed
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Old 7th Jan 2013, 2:23 pm   #178
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Default Re: Building an oscilloscope at home

In this link you can download a short video showing how the sawtooth is synchronized with an input signal.

http://www.ziddu.com/download/212852...05652.AVI.html


Quote:
Originally Posted by jhalphen
your scope with a dying CRT is the C1/94, correct?
Yes, it is.

Quote:
Originally Posted by jhalphen
Can you please give me the CRT model in this scope
8ЛО7И

Weight: 400g
Lenght: 250mm
Diameter: 78mm
http://www.radiolamp.ru/sprav/elt/8lo7.html

Don't worry about this scope (C1-94). I'm not really interested to fix it.
I would be more interested to get a CRT of the type used in the C1-124 scope that I'm using, lent by a friend.

Quote:
Originally Posted by Ed Dinning
now that only Miguel is building scopes anymore.
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Old 7th Jan 2013, 4:11 pm   #179
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Default Re: Building an oscilloscope at home

I forgot to tell you something that I did this weekend. I tested an EF80 replacing the 6BW7. It worked very nice.
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Old 8th Jan 2013, 12:17 pm   #180
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Default Re: Building an oscilloscope at home

Hi Miguel,

I looked up the Russian C1-124 scope and found this:
http://translate.google.com/translat...69%26%2FS1-124

Apparently a 10 MHz single channel scope.

Do you have the model of the CRT it uses?
Is that the one you want?

Please give the reference in Western characters, not Cyrillic ;-)

Best Regards
jhalphen
Paris/France
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