Please Help My Tube Microphones!

[northsiderap]

Hey All....

You've all helped me in the past, so here's another one:

I have two tube microphones, and they both have developed the same problem.

When I turn them on, it sounds 'windy,' referring to the sound of the noise that is made. Of course this noise is bad. When I switch the power off, the noise goes away and the mics are fine for 15 seconds or so while the capsule and capacitors bleed dry.

Is the problem:

A) Bad/Leaky/Microphonic Tube? (one mic is fairly new, the other @30 years old...)

B) Power supply filter caps?

C) Microphone capsule with obstructions which leak capacitance from diaphragm to backplate?

D) Something else...

Any advice would be appreciated, because I will be fixing them myself even if I have to replace each component one at a time (starting with capacitors & tubes)

They are both basic tube mics with a single tube and transformer audio chain....

Get as technical as you want with your answer (and more) because I will be doing this a lot in the future.

Thanks for everyone's great help sofar,
Jim
**Northsiderap.com**

[Tekko]

What tube are they using ? Got any pics ? It could be A, B would be a huummmmm, C would be more a low volume (need to talk closer to mic) like when you overheat a condenser mic capsule soldering leads to it.

[dhaen]

Where do they get power from? A common source?

[northsiderap]

The Mics:

One of them is a VERY old Vega Capacitor Microphone which was used originally by drummer Billy Cobham and takes a 6cw4 RCA Nuvistor. The power supply is only caps, audio transformer, power transformer, rectifiers, and resistors. Yes, I do have a new 6cw4 RCA on order already.

The other is a GTAM62 by Alesis (Groove Tube). Takes a military-spec sub-miniature tube. Haven't looked into the guts of the power supply on this one. I think the problem is in the mic, and I will be starting with the tube there, too.

I just thought it was odd that both mics came up with the same problem being so different in age.

The Noise:

The noise is not just hiss, it sounds like wind. It varies in intensity, it literally sounds like a nice breeze blowing on the microphone as if you were recording outside...

The power comes from a standard wall plug. I'm not worried about power distortion, because my father is pretty much an electrical engineer and has reviewed my wiring. I've tried different tube mics on the same outlets as well. No problems with my other tube mics, including an identical GTAM62..

Thanks again,
Jim
**NorthSideRap.com**

[Enzo]

I just had to replace one of those little 5640 tubes in that mic. It was beyond noisy though, after a minute or so it would load down the B+. Groove will sell you the tube through a dealer, or find one elsewhere.