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Old 17th May 2012, 10:18 am   #61
RF Burn
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Default Re: Building an oscilloscope at home

The oscilloscope is still a very important and useful instrument to equipment designers and service engineers, in my job as an embedded software engineer I could not manage without a 'scope for letting me 'see' what is happening when debugging and verifying the operation of my code. Modern professional 'scopes are very sophisticated in their abilities, certainly not cheap, and - in my experience - definately not being given away!

That is not to say that there is not 'cheap' equipment available more suited to experimenters and amateur users, however, I believe that the word 'cheap' must be qualified by the level of financial income and there is also the issue of local availability - two areas in which we are blessed here in the UK.

I wish you much success in your endeavours Miguel!

Adrian.
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Old 17th May 2012, 4:28 pm   #62
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Default Re: Building an oscilloscope at home

Thanks to all of you for your kind words. I hope to be able to go on with this project until the end.

Quote:
Originally Posted by val33vo
but why would anyone contemplate building their own scope? If you go to any ham jumble sale you will find they are virtually being given away free
Reading this I understand that you know absolutely nothing about Cuba.

To buy a scope? With what budget?. Let me tell you as an example that in my enterprise we still use scopes from the Soviet era. Scopes are not sold in the shops here. Even if they would be sold, they would be beyond my financial reach. A scope can cost the equivalent to the salary of six month of work here, and I'm talking about a used scope from the Soviet era. If you want a modern oscilloscope (analog, not digital) it will cost more than the money I will earn in my entire life. My Soviet C1-94 is almost dying, and I need a replacement. I can not buy it, so why not to build it.
For further questions and/or explanation about this situation, please PM only.

On the other hand, you should experiment the feeling to build something with your own hands, skills, and knowledge. It is a great joy when at the end of the road you can say: Damn, I did it !!!!!

And definitively, I will learn a lot of new things doing this.
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Old 17th May 2012, 8:12 pm   #63
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Default Re: Building an oscilloscope at home

Are EF37 suitable for the input stage of a simple scope?

http://www.r-type.org/pdfs/ef37.pdf
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Old 18th May 2012, 11:01 am   #64
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Default Re: Building an oscilloscope at home

They should be good. Have you got some. I think a lot of still existing ones in the UK have been used up in rebuilding the Colossus computer.
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Old 9th Jul 2012, 5:00 pm   #65
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Default Re: Building an oscilloscope at home

I did some test with a high voltage oscillator and I got a very strange pattern. Has anybody any idea of this? Could the scope failed?

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Old 9th Jul 2012, 5:38 pm   #66
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Default Re: Building an oscilloscope at home

Where was the scope connected? How much HV voltage are you trying to produce, and have you considered a voltage mutiplier rather than an oscillator to perform this function?

Peter
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Old 9th Jul 2012, 6:24 pm   #67
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Default Re: Building an oscilloscope at home

The scope probe was connected across the output winding of the transformer. In fact across a 10K resistor connected in series with a 110K resistor and this arrangement was connected to the output winding. This winding was floating (un-earthed)

The output winding was only intended for test and it produces only a small fraction of the voltage needed. 100V more or less.

What I need is +4000V DC and -1500V DC to supply the CRT I have.

I intend to use this oscillator with a voltage multiplier in the output, but as capacitors are small (1000pF), I want to increase frequency. That's the reason for the oscillator.
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Old 9th Jul 2012, 7:20 pm   #68
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Default Re: Building an oscilloscope at home

Hi Miguel

Pushing up the frequency means that you need faster high voltage diodes. Generally available ones for TV use will let you use up to several tens of kilohertz with good efficiency. A lot of 100v general purpose rectifiers are so sleepy that they have switching time-related problems even at 100Hz.

Cheers
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Old 9th Jul 2012, 8:30 pm   #69
Miguel Lopez
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Default Re: Building an oscilloscope at home

I've got HV fast diodes, Soviet 2Ц106А. Diodes are not a problem, capacitors are.

Any idea on the oscillogram, please?
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Old 9th Jul 2012, 9:55 pm   #70
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Default Re: Building an oscilloscope at home

You seem too have something getting into the X amplifier or timebase. That certainly isn't a normal scope trace!

David
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Old 9th Jul 2012, 10:53 pm   #71
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Default Re: Building an oscilloscope at home

It looks like rectified mains on the Y and a sine wave signal one on the X with the timebase on as well so not quite in X-Y mode.
Can you get a normal trace on it?
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Old 10th Jul 2012, 10:22 am   #72
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Default Re: Building an oscilloscope at home

I agree it looks like you are getting some stray signal on the X as well as the timebase.

Going back to the HV supply, if you have some .015uF 630V capacitors it is possible to provide both the 2KV and 4KV using the 2Ц106А diodes you have from a single 300Vac 50Hz source, (less then 300Vac with more stages).

See the diagram which is from a homemade scope (not mine) the circuit provides -2KV.

You can also run another voltage multiplier from the same 300Vac source to give you the +4KV needed. See the other diagram which shows a multiplier for both + and - HV from a single source.

Of course it all depends on you having the capacitors.
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Old 30th Jul 2012, 9:37 pm   #73
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Default Re: Building an oscilloscope at home

Definitively the C1-94 is out of service. I had to dedicate a time to fix it (again).

The oscillator circuit work very good, giving a nice sine wave in the output winding. Initially it was tuned at 300kHz, but I think it is too high frecuency, and adding a capacitor to the grid circuit acroos the wnding conected to the grid, the frecuency fall to 40kHz. I still think that it is a very high frecuency.
What do you think?

The oscillator stopped working with a capacitor of around 0,1uF.

I'm thinking to make a 1/3 Hartley oscilator with an iron transformer in the non-tuned plate, working at 10kHz to get the desired voltage.

PS. I used a scope in my job to see the trace.
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Old 31st Jul 2012, 8:10 am   #74
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Default Re: Building an oscilloscope at home

I'd pick a frequency between 20 and 30 kHz, then you can use a TV line output transformer core, and TV HT rectifier diodes will be fast enough.

10kHz risks making the thing irritatingly audible.

Back in the 1960s I used to use a 50Hz iron 400-0-400 transformer driving a Cockroft-Walton multiplier (the circuit posted in number 72, above) to make -2kV for my VCR97 tube. The capacitors were 0.1uF and about 50mm diameter by 150mm long. I never thought of a high frequency oscillator. It would have made things a lot simpler, and I'd taken a lot of dead TVs apart for the components. I must have been stupid. All the clues were there.

Cheers
David
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Old 31st Jul 2012, 6:55 pm   #75
Miguel Lopez
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Default Re: Building an oscilloscope at home

Quote:
Originally Posted by Radio Wrangler
I'd pick a frequency between 20 and 30 kHz
Can an iron transformer work at such frecuencies?

I intend to use this tranformer (in the plate of the tetrode) to get all needed voltages, except for the heaters, which would be supplied by another transformer.
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Old 31st Jul 2012, 11:43 pm   #76
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Default Re: Building an oscilloscope at home

An iron transformer could work at these frequencies but it would be quite lossy unless the laminations were very thin. A ferrite core tenderly ripped from an old TV LOPT would be a lot better and free.

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Old 1st Aug 2012, 3:24 pm   #77
Miguel Lopez
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Default Re: Building an oscilloscope at home

Is there any formula to calculate how many power can be transferred using a ferrite core? Approximately unless?
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Old 1st Aug 2012, 4:44 pm   #78
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Default Re: Building an oscilloscope at home

There is an excellent article on electromagnetics here: http://ludens.cl/Electron/Magnet.html
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Old 1st Aug 2012, 4:54 pm   #79
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Default Re: Building an oscilloscope at home

Quote:
Originally Posted by Radio Wrangler View Post
Back in the 1960s I used to use a 50Hz iron 400-0-400 transformer driving a Cockroft-Walton multiplier (the circuit posted in number 72, above) to make -2kV for my VCR97 tube.
Hi, this thread is being very useful to me as I have the parts from a home made scope ( not made by me ) and I think it uses a vcr97 crt.
at the time I got it I thought about making a multiplier to increase the EHT voltage.
regards Peter B
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Old 1st Aug 2012, 9:32 pm   #80
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Default Re: Building an oscilloscope at home

Hi Peter, if you let me know the valves etc used in this scope I may be able to find the circuit/ artilce for you. Please note, however, that increasing the EHT will give a brighter trace at the expense of deflection sensitivity, hence most modern tubes now use PDA (post deflection acceleration).

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