Electrostatic Speakers/SS amp - what tube preamp?

I will third the SF recommendation.

Gilbert Yeung at Blue Circle loves Martin Logans, and uses a pair of Odessey and a pair of CLS (amount some other brands) to tweek and test his designs.

His pair of CLS are pink (a custom job just for him by Martin Logan as a joke).

So put his tube preamps on your list. The matching amp to his BC21 and BC21.1 preamps is a solid state amp (BC22). Many also use his BC3 preamp with either a BC22 or a BC26.

Just curious. Do the Blue Circles have a balanced option?

Unsound, I'm realy curious about 50Ohms...
If that is the case or near arround even SF can be an issue of compatibility. I might be wrong if SF is transformer-coupled like AN...?

Marakanetz, Why to you feel a 500 ohm out put pre would present a load problem for a 50K ohm input? This is a 100 to 1 ratio. As i recall the minimum is 10 to 1. I would expect that the best thing a user could do would be to ask the manufacturer of the pre amp (if it is not specified in the user manual, as mine was).