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Re: Citation II AC balance

Just a thought - since one tube already is inverted (due to the action of the phase inverter stage) simply summing will work even better. Get the no-signal traces to overlap as accurately as you can, set both channels to the same scale (I use 1-2 volts and AC couple the probes).

Then when you sum/add the two forms your goal is to get as close to a straight line as possible.

If you invert one scope channel you are "undoing" the phase inversion already present. Don't invert one channel, you'll see the improvement in the procedure right away.

TOP SECRET HINT! - Shhh, don't tell anybody I told you...

After you get the straightest line possible on your scope rotate the balance pot clockwise (as viewed from the top) about 2 widths of the slot in the pot shaft. This will give a tad more THD, but a much nicer distortion spectrum - a "waterfall" pattern, if you will, with each higher order lower in amplitude than the one before.


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