Bob wrote:

My newer design approach is to use a switching ring of FETs, but the results
still can't match up to the 7360.
Do you use the fets as passive switches, or do you apply power between
the source/drain? What kind of fets (IE: depletion mode jfets or
enhancement mode mosfets)?

Can you post the 7360 mixer circuit you use somewhere?

BTW these tubes (7360, 6AR8, 6JH8, 6ME8) are sensitive to magnetic
fields and need to be shielded for best results. James Millen used to
make a mu-metal shield that would fit over tubes this size. I would
suspect unshielded tubes could be the reason for the poor results
obtained with some of the color tv versions of these tubes.

Also the 7360 is shown as a tetrode, while the color tv tubes are
pentodes (ie: they have three grids), but grid #2 is grounded and grid
#3 has normal 'screen' voltage applied. Grid #2 is internally connected
to the heater or cathode for these tubes.