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Old 9th June 2006
Lives for gear

Originally Posted by JohnnyPraze
The noise is constant. When I speak in the mic my voice sounds clear and fine but you hear a constant backround noise.

Could the mic or tube be bad?
Likely it is the tube. They often make "whooshy" or crackling noises when they are failing. Here's some information about that tube, looks like this?

"The tube is a hand-selected, pre-aged, subminiature Raytheon 6418 triode. Mounted near the bottom of the mic, it is connected by whisker-thin wires soldered to a PC board below it. The rest of the amplifier components, voltage converters/regulators for the plate and filament (and output XLR) are on this board. To prevent tube microphonics, the peanut-size triode is surrounded in foam and shock-mounted in a brass block."

This is somewhat similar to the M 149 approach. A little challenging to replace, it's not just a plugin. The tube itself shouldn't cost over a few $, if you can solder and have some fine tools it can be done, else you might want to check with AT for some service options.