PI trimmer and tube mismatch

[mcinku]

How do they say... "A picture is worth a thousand words"


http://www.youtube.com/watch?v=8lNuu7TzzNU

[CHIP]

mcinku,
The yellow trace and red trace are each PI plate and the green is the 1k signal. Is this assumption correct?

[mcinku]

mcinku,
The yellow trace and red trace are each PI plate and the green is the 1k signal. Is this assumption correct?

Well you are correct about yellow and red... those are PI plate AC signals which are 1kHz.... the green signal is the sum of both... and the goal is to make it DC if you wish

[Structo]

Thank you for that.
It's nice to have a visual representation of what we have been discussing.

[CHIP]

Thanks, mcinku
That short video really made this whole discussion alot clearer for me.

[mcinku]

You're welcome guys...
...It feels good when I'm able to give something back...even if it is a small thing like this.

[Drumslinger]

so looking at the scope, if i see the 1k signal looking like dolly pardon then i need to adjust the trim to where the PI is as flat as possible?

[greiswig]

so looking at the scope, if i see the 1k signal looking like dolly pardon then i need to adjust the trim to where the PI is as flat as possible?

I think it depends on the scope. On my scope, summed mode only results in one trace. On this scope, it looks like there are three traces. But yes, what you're after is that the summed trace is flat, because that means that the waves are effectively canceling each other out. That is AC balance defined. But it still, from what I understand, may not be the "sweet spot."

The good news is from what I can tell this should get you in the right ballpark to start looking for it by straying slightly from this point in one direction the other.

[Drumslinger]

aaahhh....ok, gotcha! use it as a good starting point and then tweak by ear to find the sweet spot.