I'm pretty sure this sound indicates a bad tube, I have edited it so you don't have to sit through the whole episode.. but after about 5 minutes the mic starts to sputter and make noise, then gradually increases the noise, the edits are about 5 minutes apart... Thanks for any insight you may have, especially the best place to get replacement tubes.
I had a ground noise Problem and it sounded the same and the noise was also increasing like on your example. Try to put shielded cables through out the whole chain. Put the mic to an other preamp, plug the Powerplug to an other powersocket, and so on...
Thanks for the reply, I am using the shielded Sony tube mic cable, I think it's 9 pins, and the power supply is connected to a furman power conditioner, and the output of the mic power supply is connected to the Neve 1064 with a Mogami mic cable, and it makes the same noise no matter what cables I use or where I plug it in.
Sometimes that noise can come from a bad contact between the tube and the tube socket. Remove the tube, clean the pins with a contact cleaner and a clean old toothbrush. While it is still wet insert it into the tube socket and gently move the tube around in the socket. Remove the tube and clean it again. Let it dry and install it in the mic. That will help remove any of the oxidation that may have built up in the socket.
If you have never taken the C800G apart to replace the tube, be warned that it's not a simple matter. If you had done it before, you would not be suggesting toothbrushes or whatever. I am sure it's a matter of replacing the tube and your problems will be gone. Be aware of the fact that Sony uses the smaller version of the 6AU6 tube inside the body of the mic and you'll need to replace it with the same form factor. These tubes are usually available for reasonable money on ebay however, finding one quiet enough to work in a microphone is a challenge and a crap shoot. If they are still available from Sony, (they used to be) I would buy one directly from them. They are selected and noise tested and expensive but........you will be done the first time. Best of luck.
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I totally agree with Charlie. Just to moreover remark that the original tube used by sony has a different shape that the regular with the same nomenclature, and as he sais, replacing the tube in the sony is quite tricky.
The tubes that I have replaced in the Sony mics have been a larger 6au6 foreign variant. The smaller NOS 6au6 is quite noisy in these circuits. Sony sets the tube at a high B+ voltage (235vdc loaded, 275vdc unloaded) thus the high failure rate. I set the voltage on my Akita microphone at 220vdc unloaded and the voltage drops to 165vdc loaded. I have not had a single failure rate on the tubes. I have several hundred of these tubes and have found them to be very quiet with a very low reject rate.
The tube is somewhat difficult to replace on the Sony because of the amount of disassembly and they have a copper foil and heatsink/thermal paste covering the tube.