Aw Well,
I may be mistaken but it would be a bit bulky to say the least to build a tube and all the assoicated electronics into a microphone! As one that has been fiddleing with electronics since the 60's you probably won't find a Mic with a tube built into it that works very well! SO, we are talking about a tube pre-amp, used with condenser microphones because the output from the condenser Mic is very weak. The next thing we need is well shelded cable so outside spurrious noises don't leak into the applied signal. In the usual application everything is shelf ready so all you have to do is plug it in and viola!, you are in business. Well designed tube circuts, work perfectly Ok in the audio application and have been for many years. As long as those designs aren't compromised in today's offerings.

Anyone that has looked in a tube amplifier lately will see metal sheilds on pre-amp tubes to prevent outside signals leaking into the circuts.

Ray E. Strode