searching balanced Tube preamp with.......

There are several that should work. The Sonic Frontier preamps all have low output impedance, with the Line 3 I believe dipping just below 100 ohms. Ralph's Atmasphere preamps should be able to drive just about anything. VTL 5.5 is also pretty low, and I am sure there are others. My guess is you don't absolutely need to go as low as 100 ohms, but what you must watch out for are the preamps that have low output impedance in the midband frequencies, then a dramatic rise in output impedance in the bass frequencies - these will roll off the bass and will not sound as good. I had similar matching issues with my McCormack DNA 500 that has 10K ohm input impedance.

Mitch2 that's what I'm looking for, to match with ss 20Kohm input impedance and not detroy the bass frequency.
I'd like to have tube preamp but so far there are not many canditates and also is not easy to know the output impedance in all frequencies.

Atmasphere is looking good but no dealer in over 700miles.
I also saw VTL 6.5 and 7.5 with low output impedance but I don't like their sound.

VAC is also a canditate.
Sonic frontiers are out since I'm looking for existing company product.

With 20k input, you will be fine with any preamp below 350 or so. No sweat.

Arthur

Many tube preamps have a low output impedance that will drive 20K- but not at all frequencies. This limitation is imposed by the output coupling capacitor. The problem is, the bigger you make the cap so it can play bass, the less transparent the cap is. There are several preamps that use output transformers, such as the EAR and Shindo, but the issue that you face then is that transformers also obscure detail and can cause a loss of low frequencies as well.

It *might* be possible to have a technician increase the input impedance of the transistor amplifier in some way. That would widen the doorway of what's possible.

700 miles- you must be in the southeastern part of the country.

I found that Einstein the tube has also low output impedance (50ohm).