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Author Topic: U47 tube - much noise  (Read 2004 times)


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U47 tube - much noise
« on: June 04, 2012, 10:03:34 AM »

I've bought a Telefunken U47 tube with original capsule (it's ok), power supply & VF14.

But mic has much noise. Where can I measure the tube voltages- mic or psu? Anyone can help me? It's the first time that I put my hands on this type of mic.


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Re: U47 tube - much noise
« Reply #1 on: June 04, 2012, 12:54:08 PM »

David Satz pointed out that I misread your post. I have therefore revised my reply:

Start with having a qualified technician measure proper supply voltages: 105VDC B+ from the power supply should translate into roughly 32-36VDC at the plate of the tube.

If the B+ generated by the power supply is out of spec, have the technician switch out dropping resistors in the supply to get it into spec (supply voltages measured under load, of course).
If the plate voltage is below 32VDC, the tube is not healthy.
If both voltages are within specs, remove the tube, and re-insert it after applying a drop of Caig De-Oxit or Pro-Gold to each of the eight tube socket contacts.

Please report back after you've done the above.

Klaus Heyne
German Masterworks®
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