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Old 8th Jan 2013, 5:40 pm   #181
Miguel Lopez
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Default Re: Building an oscilloscope at home

I prefer to talk about this issue by PM.

Thanks for your offer.
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Old 8th Jan 2013, 8:37 pm   #182
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Default Re: Building an oscilloscope at home

Quote:
Originally Posted by jhalphen View Post
Please give the reference in Western characters, not Cyrillic ;-)
Both would be best, we will all have a chance then. After all the tubes are marked in cyrillic.
 
Old 8th Jan 2013, 10:48 pm   #183
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Default Re: Building an oscilloscope at home

Just as information.

Scope.........Cyrillic...........Latin
C1-93........17ЛО2И.........17LO2I
C1-94.........8ЛО7И...........8LO7I
C1-124.......8ЛО8И...........8LO8I
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Old 21st Jan 2013, 3:25 pm   #184
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A picture of the mains transformer. It is a Soviet TCA-70-1 core. I kept the original primary winding (aluminiun) and I winded the others. The heaters winding is aluminiun too, I will fix it with screws.

I added the 20cm ruler to give an idea of the size. I tested it with full load and it kept inside the required limits.
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Old 31st Jan 2013, 3:30 pm   #185
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Default Re: Building an oscilloscope at home

Hi everyone.

I've been off-line with this project cause I was sick. Now I'm OK so I have re-taken it. Here I show some picture of what I did. One of that sections is the HT rectifier and the horizontal correction rectifier. The other is the circuitry for the EHT PSU. I included the "blueprints" too (I used blue ink )

All diodes are Soviet D226
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Old 31st Jan 2013, 5:07 pm   #186
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Glad you are bettter, the project leaps forwards (again!). I can't wait for the end result.
 
Old 7th Feb 2013, 2:53 pm   #187
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I have began with the wiring of the scope. I have already wired all heaters and power supplies. All valves already glow. I will begin to wire the circuits by these days.
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Old 22nd Feb 2013, 4:44 pm   #188
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Default Re: Building an oscilloscope at home

Hi all

I have finished to wire the whole chassis of the scope. See attached pictures. I intend to wire the EHT rectifiers this weekend. The mains transformer is not wired definitively yet, because I have to use some extra isolation for the winding that supplies the filament of the CRT, cause this one will be at -1500V

I'm eager to see a sine wave in the screen of my scope. . Lots of work to do yet.
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Old 22nd Feb 2013, 5:45 pm   #189
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Default Re: Building an oscilloscope at home

That is very impressive Miguel, very high standard of finish I like it very much.

Will you be publishing a complete set of schematics when it is fully working?

I am looking forward to seeing this finished.

What will you be using to insulate the CRT filament supplies with, plastic tubing?

Tony
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Old 22nd Feb 2013, 6:06 pm   #190
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Default Re: Building an oscilloscope at home

Hi Tony.

Yes, when finished, I will make a PDF file and I will publish it. It will be hand made drawings, the ones that I'm using to wire the scope.

The CRT filament winding is in the mains transformer. I isolated from the other windings bellow using a radiographic film in two layers, above a layer of paper. Hope this to be enough. Being this transformer a two-legged one, I have to isolate it from the other column too. I wil introdude a plastic piece (1,5mm thick) between both columns. This plastic piece will be "sandwiched" between two bakelite pieces (0,2mm thick). If this is not enough, you will see the sparks from Europe

The wire also has its enamel coating which contribute to isolating, of course.

See post 184 of this thread to get a picture of the transformer. There you can see the radiographic film in the left column winding and a piece of fiberglass between both legs. I replaced this by the "sandwiched" piece of plastic
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Old 26th Feb 2013, 5:21 pm   #191
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I had to make some changes in the Y-amplifier. I decided to use the one of the Serviscope Minor (So I think I will build a Serviscope Minor with a Soviet CRT). The circuit I built with the ECC81 did not provided enough gain to supply the Y plates. Then I build the input stage of the ServMin, with two 6BW7 pentodes.

Due to this reason I'm thinking to use an EF80 in the sweep generator in order to save a 6BW7 as spare.

The ServMin uses a floating input, which I don't like, so I used part of the circuit I had mounted before (one triode cathode follower for input, plus another triode in common cathode for a little amplification), this time using one 6N1P Soviet twin triode.

The gain is amazing now. I have ±150V with an input of less than 100mV. I only need ±12V according to the datasheet of the CRT. I will adjust once everything will be mounted in their respective places.

I will show pictures by these days.
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Old 27th Feb 2013, 3:02 pm   #192
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Default Re: Building an oscilloscope at home

I have a doubt about this that I'd somebody to clear it.

When using an analog oscilloscope, sometimes the trace goes very high or very low and it disappears from the screen.

If I have enough gain, then the beam will deflect enough to "touch" the deflecting plates. What happen then?
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Old 28th Feb 2013, 7:19 am   #193
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Default Re: Building an oscilloscope at home

Hi Miguel, not a lot. No damage will be caused. This often happens if the shift pot is wound over to one side when looking at a trace with DC offset, then next time you examine another trace with no DC offset the trace has disappeared. This is one reason for fitting a trace finder botton, it reduces both X and Y scans and makes the trace visible near the centre of the screen so you can see which way it is deflected.

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Old 28th Feb 2013, 8:43 am   #194
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Default Re: Building an oscilloscope at home

It's quite normal, Miguel. The electron beam is deflected first into the conductive surrpund of the screen and then into the 'Aquadag' graphite coating of the inside of cone of the tube. This normally carries the returning beam current and the electron gun is run as a constant current source, so the current is well-controlled. The surround and the 'dag are a lot tougher than the screen itself, which is where the beam normally writes.

The bias currents in deflection amplifiers are normally a lot larger than beam currents, so the beam landing on a plate is not a problem. Even if the amplifier current was small, the effect would be self-limiting as the beam current would make that plate less positive, and so less attractive.

Deflection amplifiers have to be designed to limit cleanly.... that is without any effects lasting after the overdrive which put them into limiting has gone away.

Beam finder buttons reduce the HT or the bias current in the output stages of X and Y amplifiers, so causing them to limit at much lower swings, thus giving a picture to show where the beam was hiding. They also defeat any blanking. Because of the change in plate voltage with beam finder pressed, you'll usually notice that the focus is degraded.

Also, beam finders are damned useful when fixing scopes!

David
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Old 1st Mar 2013, 4:00 pm   #195
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Thank you very much for your answers.

Now I want to show the final circuit that I have wired. I replace the first input stage by the one of the Serviscope Minor plus an additional two triodes input to make it referenced to HT- instead of being floating.

I also replaced the 6BW7 in the sawtooth generator to keep it as spare for the input stage. In the place of the 6BW7, I use an EF80. Now I have to say that it works better. More sweep length, more stability and better synchronization.

I think that the cricuitry is already finish so I have to begin to assemble the cabinet with all the circuits inside. Still I have to adjust the ranges.
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Old 2nd Mar 2013, 12:38 pm   #196
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Default Re: Building an oscilloscope at home

I take my hat off to you Miguel,I think we're all impressed with your ingenuity and the skill you've brought to bear on this project.

I hope those forum members who sent Miguel components can see "their" bits on the circuit boards. They stick out from the Soviet components. In your experience Miguel are Soviet discrete components as reliable as their Western equivelents? The diodes on the rectifier board look a bit clunky and old to my "Western" eyes. Still it's whats inside that counts.

Lastly do you wind your coils on a machine or just by hand? Do you use old wire off an old transformer? Nice one mi amigo,very inspiring,Andy.
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Old 4th Mar 2013, 2:12 pm   #197
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Hi Andy.

Always a pleasure to have you here.

About the comparison between Soviet and Western component. I have to say that majority of Western component are better than their Soviet counterpart.

Soviet electrolitic caps are BS, paper caps are +/- but the Western are better. Soviet MLT resistors are one of the best in the world, and the diodes are not bad. Those diodes that you see are D226 taken from an old TV set. They are good but, of course, 1N4007 would be much better.

I can get some 1N4007 from burned CFL's but I like the spartan look that Soviet diodes give. Soviet transistors are a big headache, with lots of leaks and very easy to go away, and of course I prefer Western ones. Soviet valves seem to be OK.

I've tried to use components sent by the chaps of this forums wherever I could. I also hope they can find them in the pictures. Thank you and bless you all.

I have always winded my transformers and coils by hand. I thought once to make a machine for this, but it will be very time consuminfg and I don't wind a transformer as usual as I would like, so I keep winding coils by hand. I always use wire retrieved from old transformer or coils, such as the voltage coils from old counter meters.

I have began the assempling of the unit. I will show more pictures soon.
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Old 11th Mar 2013, 1:32 pm   #198
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Tomorrow there will be a year since I started this thread. I have finally assembled the unit.

Results are modest by now, cause I have a noise coming from the EHT PSU affecting the Y amplifier. I have not been able to supress this noise yet, still working on it. I did not supresses the flyback trace neither cause you can see the noise better in this trace than in the signal
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Old 11th Mar 2013, 3:24 pm   #199
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That is impressive by any count Miguel I feel sure that you will get the scope working properly in the end.

Next time perhaps a transistor oscilloscope?

Best wishes
Tony
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Old 11th Mar 2013, 3:59 pm   #200
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Quote:
Next time perhaps a transistor oscilloscope?
Too easy
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