Building My Own Oscilloscope

[Miguel López]

Sorry Ref, I did not understand. Can you explain me more?

I'm using the Telequipment S51 Y amplifier. At the input, there is a pure resistive divider. A 100k resistor across grid and HT-, and a 220K resistor across input and grid. Signal is applied across input and HT- (320K). This arrangement is for test purposes only. I intend to use another divider for the final design.

[Refugee]

The circuit you posted in the other forum did not show any resistor to -HT.
Now I know you have fitted one that is fine.
It would be a good idea to post all the voltages in the input stage with the input earthed and again with a small DC voltage applied.
We should then be able to see what is happening.

[Miguel López]

I was testing how fast the scope can sweep. My homemade signal generator is only capable to provide a 50kHz (in fact maybe 53 or 54 kHz) signal so that was the fastest signal I could apply. Anyway, I'm very happy with the results.

As the range sellector is not fitted yet, I use a 5M potentiometer as in the Serviscope Minor and I tried to get the same picture as in the C1-124.

With the C1-124 at 2uS/div, the 50kHz signal appears as a complete cycle in the screen. I was able to get that in my scope too.

Then I decided to go faster and I set the C1-124 at 0,5uS/div. The 50kHz signal appears just as a portion of a cycle. And then I was able to get the same pattern in my scope. This means that if I would had applied a 1MHz signal to my scope. This signal would had appeared showing a cycle in two divisions. That's great for me!!!

I have gotten this sweep using two 47pF capacitors in series (23,5pF). I will try with a 10pF capacitor to see if I can get a faster sweep, cause there is a point at which it simply stop sweeping, at least while moving the potentiometer.

[pwdrive]

The circuit you posted in the other forum did not show any resistor to -HT.
Now I know you have fitted one that is fine.
It would be a good idea to post all the voltages in the input stage with the input earthed and again with a small DC voltage applied.
We should then be able to see what is happening.

I think they (the resistors) are part of the input attenuator network, there's a schematic somewhere on the web, I will post a link if I can find it.

Lawrence

[pwdrive]

Said schematic (I think?)

http://bee.mif.pg.gda.pl/ciasteczkowypot...d_S51E.pdf

Lawrence.

[pwdrive]

If the amplitude of the signal is not centered on zero on AC then it points towards a differential problem as a first guess, unless there is some non linear function happening before the diff amp when the signal is applied.

Lawrence.

[Miguel López]

Said schematic (I think?)

http://bee.mif.pg.gda.pl/ciasteczkowypot...d_S51E.pdf

That is exactly the Y amplifier that I'm using. I will check the voltages as Refugee suggests and I will post it here.