Vacuum tube oscilloscope sweep generator

[SGiard]

Noted. Thanks guys!

 

[spec]

To complement what spec mentions, if you do use ceramic caps, employ exclusively class-I ceramics (NPO, COG).
Stay away from class-II ceramics. (X7R, Y5V)

Hi ST,

Yes, good point about ceramic capacitors. Just to add a bit more:

Ceramic capacitors have two overriding advantages: very low effective serial resistance (ESR) and good high frequency performance.

But, a big problem with ceramic capacitors is that their capacitance varies with temperature and, more bizarrely, with voltage. Apart from the variation with voltage, which causes distortion, they also generate other distortion; for example, in audio amplifiers, they give an odd 'brittle', 'grainy' sound

Class I ceramic capacitors are much more stable than class II, but the problem is that class I ceramic capacitors are relatively expensive, relatively large, and are not available is high capacitance vales (only about 100nF maximum).

On the other hand, Class II ceramic capacitors, are available in values up to around 47uF, so they are useful for decoupling (but not in audio amplifiers). Of the two common class II ceramic capacitors, X7R and Y5V, X7R has a better performance with temperature and voltage. So my advise is to stick with X7R, if posssible.

There is another complication though, the size of an X7R capacitor. In general, the smaller the capacitor, the worse the performance.

Just to illustrate the point, a 22uF, +- 10% tolerance, X7R ceramic capacitor may only have a value of 5uF when all the tolerencing is taken into account: 22uF *0.9 (tolerance) * 0.5 (temp) * 0.5 (voltage). And X5U is much worse.

End of sermon.

spec

 

[Les Jones]

What is the point of posting part of a previous post without making a comment about it ?

Les.

 

[spec]

Just a bit of fun really, but Here is an outline circuit for a scope trigger and ramp generator using an LMC555.

The LMC555 Q output can be used for the tube fly-back blanking.

 

[SGiard]

Thanks spec,

I'm almost at the point where I will be able to try different sweeps. Just did not have any time to work on my project lately.

 

[spec]

Thanks spec,

I'm almost at the point where I will be able to try different sweeps. Just did not have any time to work on my project lately.

No problem SG,

I know what you mean about not having enough time.

By the way, the circuit of post #8 produces a positive-going ramp. If you need a negative going ramp that can be done quite simply.

Also, the ramp in not totally linear, but that can also be sorted.

And finally if you wanted to make a complete time-base generator with precision switched an variable ranges that can be done too, although quite a few components will be required, proportional to the number of ranges you want.

spec