The RCA 88A is a pressure microphone, and is quite rare at that.  It was probably originally a broadcast mic, but I've only tried it out a few times in the recording studio for recording spoken vocals.  This is also the only non-ribbon mic that I have used made by RCA that I can think of right now.  The mic is really more of an antique now as it has been around for quite a long time and there aren't too many of them left.  However, I was fortunate enough to get to shoot one of these out with a few other mics to hear what it sounds like.  The mic has a standard cardioid polar pick up pattern and will only pick up frequencies between 60 Hz and 10 KHz, so it only has a limited versatility in terms of what it can be used to record.

OVERALL OPINION

Other than the one that I used, I haven't seen too many RCA 88As out there.  I believe that this mic was first made as early as the 1930s, so many of them have died out throughout the years.  The mic will do a pretty good job of picking up your voice, but isn't the cleanest by modern standards at all.  Since it only picks up a limited width of frequencies when compared to modern day mics, I can't say that I would recommend it for anything other than mid range applications, and namely the human voice.  Since RCA is a large brand that has a lot of classic microphones, the I would imagine that even if you did find one of these used, that I would cost a decent amount of money compared to what it was when it was originally manufactured, as I believe this was a low budget microphone even at the time.  Having said all of this, if you like old vintage mics and RCA specifically, the 88A will definitely still please you.