[Ian Iveson]

Ian Bell wrote:

Looks like there is some frequency dependent. I made
additional tests at 100Hz, 500Hz and 4KHz as follows (grid
distortion in original circuit):

100Hz 2H -63dB, 3H -65dB
500Hz 2H -58dB, 3H -61dB
2KHz 2H -49dB, 3H -62dB
4KHz 2H -46dB, 3H -65dB

Looks to me like the second harmonic rises with frequency
but the third varies little so I would guess the 2H is
coupled somehow from the plate and the 3H is probably the
onset of real grid current distortion.

Surely the grid current distortion is assymetric? That would
make it substantially even H?

It might be interesting to repeat this with a grounded
grid configuration.

Too many tests complicates confusion.

Ian