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 Post subject: How to test old microphones
PostPosted: Nov Thu 14, 2019 10:23 pm 
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I have some older microphones, vintage 1950's to 1990's and want to put them up for sale. I would like to know if they work but I don't have a lot of test equipment, other than VOM's and maybe some working VTVM's.
How best to do this?

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 Post subject: Re: How to test old microphones
PostPosted: Nov Thu 14, 2019 10:54 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Wayside, NJ Monmouth
Best way is to hook them up to an audio amplifier and speaker. While talking into the microphone, wiggle the cable to be sure it dose not have any interment connections.


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 Post subject: Re: How to test old microphones
PostPosted: Nov Thu 14, 2019 11:58 pm 
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Joined: Feb Sun 17, 2008 11:36 pm
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Location: Dayton, Ohio
Using the audio section of a SIGNAL TRACER would be handy. Ample gain for magnetic mics, a built in attenuator for high output mics. Built in speaker.

For carbon microphones and condenser microphones you will need a suitable external voltage source.

The "NOISE" test on some Tracers might work for carbon mics.

Charlie


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 Post subject: Re: How to test old microphones
PostPosted: Nov Fri 15, 2019 9:07 am 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
To test a carbon microphone, find an old dial telephone, unscrew the
mouthpiece, and take out the mike cartridge. Then clip the mike
you want to test to the contact pins.

Plug in the old phone, and get someone in the house to pick up another
phone and talk to them.

If your know that the mike you need to test is a double button type,
you don't need me to tell you how to test it.

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 Post subject: Re: How to test old microphones
PostPosted: Nov Fri 15, 2019 1:25 pm 
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Any stereo with a phono preamp could be tasked as a microphone amplifier. Since the circuit has an EQ curve for records, if it is for magnetic pickups, the sound will not be ideal but it might show function. Aux inputs are not enough gain unless maybe a crystal microphone is used. I use an O scope for basic check of output but that does not reveal how it sounds. A voltmeter would need to be AC and be able to show a few millivolts from a steady tone of some sort. That makes them much less than ideal as many do not have that much resolution. You can also go opposite and feed audio signals back to the microphone from a generator with low output, then you ought to hear a weak tone if you hold the mic to your ear like a headphone. The risk there is too much signal damaging the mic. And it does not tell you how it sounds, as a microphone. Just that the pathways work.

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 Post subject: Re: How to test old microphones
PostPosted: Nov Sat 16, 2019 1:57 am 
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Thanks. All good ideas.

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 Post subject: Re: How to test old microphones
PostPosted: Nov Sun 17, 2019 2:50 am 
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Joined: Nov Fri 10, 2006 12:24 am
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Location: Thornhill, Ontario, Canada
wazz wrote:
Any stereo with a phono preamp could be tasked as a microphone amplifier. Since the circuit has an EQ curve for records, if it is for magnetic pickups, the sound will not be ideal but it might show function...
Good idea! Turn the bass control way down and it might even sound OK... but I've not tried this as I have a mic preamp/mixer.
Cheers,
Roger

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 Post subject: Re: How to test old microphones
PostPosted: Nov Sun 17, 2019 4:27 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 11812
Location: Powell River BC Canada
With dynamic mikes, output level is the best test. However with low
impedance mikes, you must have a low impedance transformer input.

If you do not have an XLR inline transformer, you can use the one from
a junked dual impedance type with a switch.

Some mikes will need a phantom voltage. So will electret condenser
types.https://en.wikipedia.org/wiki/Phantom_p ... techniques

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