"Does anyone out there have a C6th tuning chart that indicates tuning by harmonics."
I don't have a chart Andy, but maybe some of the following will help.
1. Harmonic the 1st string at the 12th fret, and the 3rd string at the 19th fret. Tune the 1st string for zero beat. Note: Do this AFTER you have tuned the 3rd string to correct pitch.
2. Harmonic the 3rd string at the 19th fret and the 5th string at the 24th fret for zero beat.
3. Harmonic the 2nd string at the 5th fret and the 3nd string at the 4th fret and tune the 2nd string for zero beat. Note: it takes mucho practice to get these harmonics to sound loud and clear. However, it CAN be done with time and patience.
4. Harmonic the 2nd string at the 12th fret and the 4th string at the 19th fret for zero beat.
5. for the 6th, 7th, 8th, and 10th strings you can use octaves (one string open the other harmonic) to get these zero beats.
6. Harmonic the 7th string at the 12th fret and the 9th string at the 19th fret for zero beat.
This should cover the open strings. The pedals and knee levers can be tricky. It depends on whether the "pulled" strings are creating major/minor thirds and 4th's/5th's. OR, 7th's, 9th's, dim's etc.
Here is an example.
In the case of the 7th and 8th pedal or the knee lever that lowers the 3rd string, you can use the harmonic positions as above.
You can also use this for the 6th pedal when it comes to the 2nd string raise.
BUT, when you get to the 5th pedal and the 6th string lower on the 6th pedal, you got a problem.
IF, you harmonic these strings, they will be out of tune for what they are intended. Example:
Lowering of the 5th string from G to F#. This creates a beautiful 9th chord (strings 2, 3 and 5)
IF, the 5th string is NOT in tune harmonicly.
If you tune this pull harmonicly, the 4th and 5th strings will sound great when picked together, but the 9th chord on strings 2, 3 and 5 will not sound nearly as good.
So how do you tune this 5th string lower? Well you will get as many ideas as there are musicians in the world
After years of experimenting I have found the most reliable way for me is to tune the 5th string to the 4th string by placing the bar at the the 3rd fret/5th string and tuning 5th string for zero beat with the open 4th string. Others might tune it by ear. Try it either way or you may come up with another method that is better for you.
The other pedals and knee levers fall in the same scenario. Harmonics work in some cases. In others they don't.
Now the most important note of all. If one tunes the C6 neck to straight 440, NONE of the above is true. AND to some players, it is a better averall compromise than using harmonics.
Good luck and God bless you with it,
carl