So, you like Condenser Microphones. Sony C-37A Homebrew.

Plain, simple and easy to build.
The Sony C-37A microphone in it's original form is one of the nicest sounding condenser microphones I have ever used. They are commanding some fairly high dollars these days and in the spirit of this, and being on a budget and loving to build stuff, I reasoned I could build one for a fraction of today's inflated prices.
Go on Ebay and find any Joe Meek JM-47 "Meekrophone". This is a fixed pattern Cardioid condenser mic that usually costs between $40 - $100 bucks depending on who is trying to put the toothpaste back into the tube. Plain and simple, it is a cheap bargain mic that has one good quality...it's capsule is good. Despite what you hear from people "in the know" these capsules sound pretty damn good if two criteria are met. Couple it with a good vacuum tube head amp and an excellent transformer and you have yourself a microphone that sounds as good if not better than ones costing hundreds of dollars more. Granted, if you really want to ratchet it up a few notches, an Austrian made Tiersch re-skinned capsule would be ideal but that goes beyond the scope of this project.
The fun part about this project aside from building it, is the hard work has been done for you already...the mechanics. The microphone body and associated metalwork is already there, so all you do is strip the electronics out and start from scratch. You will also have to build a power supply for it that contains both the DC heater and HV supplies. The microphone itself will require an inexpensive 6AU6 Pentode and 7 pin socket. Again, ebay can be a cheap source for these items if you don't have them already. If a supply is purchased online, then all you have to do is mount the output transformer for the mic inside the supply as the mic circuit is a Cathode follower type, and therefore does not require the transformer to be mounted inside the mic body. You will also have to re-address the microphone cable pins accordingly. I used 5 pin XLR male and female types.
Google Sony C-37A schematic and you should find all of the info you need. I like the microphone
transformers made by Cinemag here in Los Angeles. They are very excellent and are not expensive like the Jensen, or Lundahl types. Vintage UTC or Triad units are excellent too but can be expensive to source. The photos included here is an example of my work and these mics have been used on numerous recordings with very satisfying results. From time to time, I employ them on-air and they sound quite good. I should point out here, that filtering of the DC Heater Supply is very critical for low noise. Nothing is more nagging than noisy filaments...120hz. Yuck.
After all of the costs were tallied, this project came in under 200 bucks for each mic. The supplies were built using the carcasses from dead switching supplies which make rather nice bulletproof enclosures. Combo filament/plate power transformers that give you 6 volts and 120 to 250 volts @ 50 ma are quite satisfactory. You don't really need a lot of HV to operate the tube, but I have found that if you operate it at close to it's published ratings, it gives you the best clean headroom.
In actual use here, 175 volts works great. You will be amazed at the articulation and frequency response of this little guy. I should point out here, that the transformer shown below is not a Cinemag type. It is a vintage unit I used in the first one I built. The Cinemag will suffice very well.