what's the difference between condenser, valve and tube mics?
The diaphragm in a condenser microphone is one plate of a capcitor. When sound waves strike the diaphragm, it moves proportionally. The other half of the capactior is a fixed back plate. This mechanism enables diagphragm movement to generate a corresponding voltage. The voltage is then amplified and buffered
by the microphone preamplifier.
A "valve" mic is a tube mic, given that "valve" is British slang for the vacuum tube.
Earlier condensor mics required tubes for power supplies to provide bias voltage to the backplate, and for preamplification.
Fixed charge condensor microphones can be equipped with tube or transitor preamplifiers.
Am i right in understanding tube mics are better than the other mentioned types?
Not necessarily. There are many outstanding condensor microphones
equipped with solid state preamplifiers, as well as poor microphones that are equipped with tubes.
There are many other factors in microphone design that are far more important than preamp construction, assuming that the preamp, be it tube or solid state, is well designed and implented.
if so, what tube mic would you recommend for professional studio quality recordings (mainly vocals) within the $0-700 price range?
I can't personally recommend any tube mics in that price range, though I suspect there are a few decent ones out there.
Be aware that tubes are often used as marketing gimmick in low priced audio gear. Go try a lot of different microphones, be they solid state or tube, and find a mic that has the right combination of perforamnce (frequency response, self noise, pattern uniformity, sensitivity, desired pattern(s), good off axis response. rf immunity, etc.
There are a number of good to great vocal mics on the market, so there's bound to be at least one that is financially accessible, that works for your voice. Audition as many as you can, and use your
ears to choose! And for more information on microphones in general, this Wiki page is readable and accurate:http://en.wikipedia.org/wiki/Microphone#DC-biased_microphone_operating_principle
There are some really good texts on microphone theory and use, such as:
The Microphone Book, Second Edition by John Eargle
Modern Recording Techniques by Robert Runstein used to have a very good chapter on microphones, don't know if it still does.
Good luck with the hunt.