Building My Own Oscilloscope

[Miguel López]

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.

[Yorkie]

Thanks for the update Miguel and for keeping us up to date with all the pictures. What an amazing project this has turned out to be - at least if it develops a fault you'll know your way around it!

All the more remarkable in that you don't have a workshop, but have to do the best you can in your ‘all in one room’, which - as you describe it - has you bed, the TV and your workbench.

To say 'well done' doesn't come even close to the recognition you deserve for your efforts.

[Miguel López]

To cut metal , I go to my parents house, in other town. There my father built a shed with several homemade tools inside (like father, like son). he was a mechanic and so I have there a bench drill, a big wise, an electric emery wheel, and a sheet cutter (all that home-made as said above).

The electronics work (mounting, soldering, adjusting), I do it in my all-in-one room.

[Miguel López]

Finally I have 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 supressed the flyback trace neither cause you can see the noise better in this trace than in the signal

[Refugee]

Those EHT units are normally enclosed in a metal can in order to screen them.
The plate wires are not that far away from the transformer.

[Miguel López]

I've been simulating some circuits to get high voltage EHT to power the CRT, and preventing noise to reach the Y amplifier

To get the -1,5kV, I'm thinking to rectify 600V AC 60Hz using a bridge rectifier. As I have -600V to supply the sawtooth generator, I will add in series this voltage with that one to get around 1,4kV. That's enough for the CRT according to datasheet.

This circuit will have a ripple.

For the +4kV I want to use a voltage quadrupler from an 850V AC winding. The output will be around 4kV according to simulation.

This circuit will also have a ripple.

My doubt is about the ripple.
How do both ripple could affect to electron beam?
Will a see a dotted line in the screen instead of a hard line?

[pwdrive]

Hello Miguel, I am no expert but I would have thought that the ripple on the cathode supply is the most critical.

Lawrence.

[Miguel López]

The cathode is supplied by the -1,5kV. I can reduce that ripple by adding more caps (0,47uF/1000V).

[pwdrive]

Yes, it would be easier to reduce the 1.5Kv line ripple than to reduce the 4Kv line ripple unless you can increase the available feed current through the quadrupler to compensate.
I suppose you will just have to try it and see what real effect any ripple has on the CRT display.
I built a 'scope many years ago using an old 3BP1 CRT, the EHT demand was not as high as yours but I do remember that the CRT supplies were mains derived (UK 50 Hz) and I don't recall any ripple effects on the CRT display.

Good luck.

Lawrence.

[boiss]

Many years ago I came across some EHT units.these were voltage multipliers with a 2 transistor oscillator and a toroid.
Input 12V DC, Output frequency 30KHz (and 300V from the Toroid), this was then multiplied up to 20KV for a TV monitor. This was a Marconi design for a broadcast quality B/W monitor. The transistors were BFY51.
Maybe simpler, much cheaper and certainly lighter than the 50Hz iron etc. My Solartron scope uses a 2 transistor Osc too although the output voltage is somewhat higher, this then has a tripler to bring it up to 4KV. Frequency is a bit under 20KHz. and is rather annoying. Certainly at the higher frequencies ripple is less of a problem and the tube capacitance also helps I guess.
Mike