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Q. How do I take care of my valve mic?

The Oktava MKL2500 valve mic uses a 6C315P vacuum tube.The Oktava MKL2500 valve mic uses a 6C315P vacuum tube.I've just got hold of an Oktava valve mic. Having not used one before, I was wondering if there are any general rules or guidelines I should be aware of when using valve mics. Is it harmful to leave the mic powered up for long periods of time — a whole day, say — or should it be used just for the times you need it?

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Technical Editor Hugh Robjohns replies: I have a couple of 'do's and don'ts' for you.

  • Never disconnect the mic body from its dedicated power supply unit without turning the power supply off first, and never switch on the supply unit with the mic disconnected.
  • Never drop the mic (obviously!), and be very gentle with it for a few minutes after it has been switched off. It's usually best to leave the mic to cool off completely before disconnecting, dismantling and packing it away!
  • When you first power it up, allow up to five minutes for the microphone to warm up and fully stabilise before making any critical recordings.
  • Valves do age over time and will eventually 'wear out', although this is an extremely slow (and often subtle) process. Changing valves is not particularly difficult in most cases (it's best to refer to the manufacturer's guidelines for instructions on how to do this) and new valves needn't be expensive, but it pays to use high-quality valves.
  • If you are using the mic on and off throughout the day then I would leave it on the whole time. If you are using it for a recording in the morning and then maybe again late at night, I'd probably turn it off in between times.