21st Mar 2012, 2:56 pm | #21 |
Heptode
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Re: Building an oscilloscope at home
Thank you Bill
Saddly I'm not allowed to access such sites. If you can share the scans, I will appretiate it.
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21st Mar 2012, 3:51 pm | #22 |
Hexode
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Re: Building an oscilloscope at home
Hi Miguel,
The Cossor 1039 (manual attached) is a very basic 4 valve oscilloscope. It should be quite simple to build something like it. |
21st Mar 2012, 4:14 pm | #23 |
Hexode
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Re: Building an oscilloscope at home
Hi Miguel,
The Telequipment s31 is a good little oscilloscope, it has a proper triggered time base and the vertical amplifier is OK up to 6 mHz. |
21st Mar 2012, 4:20 pm | #24 |
Heptode
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Re: Building an oscilloscope at home
Thanks n_r_muir.
Very simple indeed, the 1039. It looks suitable for my purposes. I'll see if I can replace those tubes with any Soviet, or with any sent by my friend Andy. I have several Soviet 6J5P, equivalent to the 6AH6. And Andy will send me a couple of EF80. Don't know if they could be suitable for replacement. The S31 uses too many valves and it's too complex for a beginner like me. And the valves will be hard to obtain.
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21st Mar 2012, 5:43 pm | #25 | |
Heptode
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Re: Building an oscilloscope at home
Quote:
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21st Mar 2012, 6:52 pm | #26 |
Hexode
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Re: Building an oscilloscope at home
Hi,
I expect that the scope will work well enough if you build it with ef80's instead of 6am6's |
21st Mar 2012, 7:23 pm | #27 |
Nonode
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Re: Building an oscilloscope at home
Here are a couple of threads with a couple of scopes from practical Wireless and Practical Electronics.
Keith https://www.vintage-radio.net/forum/...ad.php?t=64159 https://www.vintage-radio.net/forum/...ad.php?t=65714 |
21st Mar 2012, 7:32 pm | #28 |
Heptode
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Re: Building an oscilloscope at home
Thanks Keith. All files downloaded, I'll be looking to them these days.
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21st Mar 2012, 8:33 pm | #29 |
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Re: Building an oscilloscope at home
Wow!!! The PE65 is really simple, and it only uses 5 dual triode valves.
I this is the one.
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21st Mar 2012, 11:27 pm | #30 |
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Re: Building an oscilloscope at home
Miguel,
There's a lot of information on scope design in the archives of the Hewlett-Packard Journal.... to be found for free on the HP labs website if you have access. If not any of us can extract them and trim down the pdfs to just the articles you want for posting here. I've got several old HP scope tubes sitting up in the attic in their mumetal screens if anyone could get a couple out to Miguel. I can understand why he wants to build something himself, The feeling of achievement is wonderful. But I've not used these things myself, and I've got more than I need, and I've been waiting for someone who could enjoy them to come along. Cheers David
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22nd Mar 2012, 4:19 pm | #31 |
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Re: Building an oscilloscope at home
Thanks David, I'm searching on that page. Tell you later.
To build my own equipment has always been a constant in my life as electronics lover. One reason, as you said, enjoy it while building. It is a nice feeling when you finish a device and you can say: It works!!! I did it!!! The other reason, I have no choice. I've always thought I should never be able to build an oscilloscope due to its complexity and the lack of parts, but now with the knowledge I have acquired here, and with the help of all of you, I feel myself capable of doing it. If my little Soviet scope fails definitively (and it will), now I feel myself capable of find a solution like this. ************************************************* A doubt had arose to me regarding the PE65 schematic. It seems that the Y amplifier can only amplify AC signal. All amplification stages (including the input) are coupled via a capacitor. Am I right? The diagram I'm talking about is in one of the link that Keith posted: https://www.vintage-radio.net/forum/...ad.php?t=64159 Post #4, file PE65_scope_1.PDF. With those capacitors, the DC level can not be amplificated.
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22nd Mar 2012, 6:30 pm | #32 |
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Re: Building an oscilloscope at home
Hi Miguel.
If you are looking for a simple oscilloscope with a DC coupled vertical amplifier the try this one. |
22nd Mar 2012, 9:07 pm | #33 |
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Re: Building an oscilloscope at home
Hi Miguel, that is an unfortunate aspect of simple scopes, only AC coupling. Probably no really slow timebase speeds either.
I'll try and get my scans done for you next week when I'm back at work. Ed |
27th Mar 2012, 5:26 pm | #34 |
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Re: Building an oscilloscope at home
The schematic given by n_r_muir seems OK for DC signals. I'll try to make an hybrid between this one and the PE65. Thanks friends.
A friend who studied in the USSR helped me to read the 17LO2I datasheet. Unfortunately he knows nothing about electronics. I think that I've found an interesting data. The datasheet state the this CRT deflects the beam 1mm/V in the X axis and 4 mm/V in the Y axis. As the screen is 120x100 mm I will need ±60V in the X axis to sweep the whole screen horizontally and ±12,5V to do the same vertically. Are these values common for CRT? They seem a little small to me.
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27th Mar 2012, 7:49 pm | #35 |
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Re: Building an oscilloscope at home
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27th Mar 2012, 9:39 pm | #36 |
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Re: Building an oscilloscope at home
Hi Miguel, tube deflection sensitivities are usually given in terms of mm/volt at a certain EHT level. Higher accelerating voltage (EHT) will give a brighter trace, but make the beam "stiffer" and less easily deflected. This is why PDA (Post deflection acceleration) is popular as the high accelerating voltage to give a bright beam is after the deflection electrodes and so has little effect on their deflection factors.
Ed |
28th Mar 2012, 12:35 am | #37 |
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Re: Building an oscilloscope at home
Hi Miguel,
Those sensitivities are pretty good. Scope designers make the electrons traverse the Y plate area first, then the X plates. This favours the Y plate sensitivity at the expense of the X plates. The Y plates are further from the screen so the angle of deflection gives more millimetres of movement on the screen from simple geometry. Sensitivity also depends on the speed of the electrons (which depends on the accelerating voltage from cathode to the plate area. As Ed just said.) Slow moving electrons have more time between the plates.... more time to be accelerated sideways by the field, so they are deflected more... so greater sensitivity. The price for this in not good. The amount of time the electron takes to pass the plates affects the bandwidth. A fast signal will have changed polarity and will be undoing the initial deflection before the electron has passed. You wind up with a direct trade-off between bandwidth and sensitivity of the tube. The plate length versus speed versus bandwidth thing is just the same as the top frequency response of a tape-head versus its gap width and the tape speed. You get a frequency response curve shaped like (1/f)*Sine(f). There are ways to cheat. Putting a mesh into the CRT allows you to have slow electrons in the deflection area and to therefore have greater sensitivity, and to then accelerate them *after* deflection to give better brightness. PDA means post-deflection accelerator. The mesh screens the deflection area from the high fields in the latter half of the tube. Shaping the mesh and the coating inside the glass bulb can create a lens which magnifies deflection. You can get a defocused 'ghost' spot in these CRTs where a direct unmagnified part of the beam is deflected only half-way from the tube axis as is the main spot. The wildest trick is to use 'distributed plates' Take an ordinary CRT design. Consider the length of the Y plates an electron traverses. Consider the speed of the electron and the time its journey along the length of the plate takes. If I replaced the plate with a much shorter one, the bandwdth would go up proportional to the shortening, and the sensitivity would fall by the same amount. No-one said I can't fit a second short plate after the first one. If we feed it with a delay line, to delay the signal to match the time the electrons take to move from one plate to the other, the deflection effects will add up, doubling its sensitivity WITHOUT costing use bandwidth. We can build a whole series of small transverse strips for plates, with a tapped transmission line to set a series of delays. We get the sensitivity appropriate to a big plate, the length of our array of mini-plates, and we get he bandwidth appropriate to the length od one mini-plate. A win-win situation! The same trick can be used on deflection amplifiers by using many vacuum tubes or MOSFETS in a 'distributed amplifier' Cheers David
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28th Mar 2012, 8:18 pm | #38 |
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Re: Building an oscilloscope at home
HI Miguel, attached is the simple scope circuit from Practical TV, dead simple, but AC coupled. The valves can be EF80, EF50 or any RF pentode.
Ed |
28th Mar 2012, 8:21 pm | #39 |
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Re: Building an oscilloscope at home
Hi Miguel, a better circuit this time from WW; and DC coupled. No valves, but common op amps and the HV transistors are TV video amp types.
Ed |
29th Mar 2012, 3:24 pm | #40 | |
Heptode
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Re: Building an oscilloscope at home
Thanks a lot to all of you. I will download the PDF files to study.
Quote:
Bandwidth is not a problem. I do not intend this to be a super oscilloscope. I'll be glad with 200kHz. I have only used my C1-94 up to 1 MHz once, when I built the first digital clock using a 1MHz xtal. I always use the scope in the AF bandwidth and mostly to measure 60Hz signals from the mains.
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