{Collins} Re: KWM2A Microphones



Just a note, beware of matching transformers as they are very prone to 
induce hum.  The best approach is the Astatic T-UG8 Stand which has an 
active stage in the base that has a very HI-Z input.  It will drive just 
about anything down to 100 ohms.  When used into an input such as the S Line 
series of radios it appears as a voltage amp.  Very clean, no hum.  Just set 
the Collins mike gain at about 1 o'clock and adjust the preamp gain for 
desired ALC action.  These preamps have a FET input with a Z in the 10 
megohm range.  Frequency response is flat from near DC to daylight (well 
over 100 KHz) and the noise is some -75 dBu.

73
Bob, K4TAX


----- Original Message ----- 
From: <dgsvetan@xxxxxxxxxxxxxxxxxxx>
To: <wa7fab@xxxxxxxxxx>
Cc: <collins@xxxxxxxxxxxxx>; <XE1YZY@xxxxxxx>
Sent: Thursday, October 21, 2004 4:48 PM
Subject: {Collins} Re: KWM2A Microphones


> Van,
>
> With all due respect, I have to say that "Hi-Z" is a relative term.  Ye=
> s,
> some folks, when talking modern solid state gear, might well consider 6=
> 00
> ohms as "Hi-Z".  Not so for the tube gear.  Check out the manuals and s=
> pecs
> for Collins, and other, vintage tube equipment.  You will see that the
> correct, or desired, microphone impedance is on the order of 47 to 50
> kohms.  I have seen some numbers as high as 100kohms, and some as low a=
> s
> 20k, but these are all a lot higher than 600 ohms.
>
> You are correct in that running up the mic gain may produce desired out=
> put.
> However, you are also leaving open the possiblity of more hum and
> extraneous noise to appear in the SSB output of the xmtr.  The previous=
>
> posting from W8RO about Z-match transformers is the correct way to go. =
> If
> cost is a factor, shop at hamfests or on ebay.  I have obtained very ni=
> ce
> condition Shure Z-match transformers for as little as $5 that way.
>
> 73, Dale
> WA9ENA
>
>
>
>
>                                                                       =
>                                                                       =
>
>                      "K7VS Van"                                       =
>                                                                       =
>
>                      <wa7fab@xxxxxxxxxx>              To:       <XE1YZ=
> Y@xxxxxxx>, <collins@xxxxxxxxxxxxx>                                    =
>
>                      Sent by:                         cc:             =
>                                                                       =
>
>                      collins-bounce@xxxxxxxxxx        Subject:  {Colli=
> ns} Re: KWM2A  Microphones                                             =
>
>                      stserve.com                                      =
>                                                                       =
>
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>                                                                       =
>
>                      10/21/2004 12:08 PM                              =
>                                                                       =
>
>                      Please respond to wa7fab                         =
>                                                                       =
>
>                                                                       =
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>
>
>
>
>
> 600 ohms is considered hi-z but all mics vary in output depending on th=
> e
> microphone element used.  And also frequency response.  Some higher out=
> put
> than others and some "tuned" for ssb communications and others for wide=
> r
> frequency response.  Just crank up the mic gain on your KWM2.  On some =
> mics
> I have it wide open!   Van, K7VS
>
>
> ----- Original Message -----
> From: <XE1YZY@xxxxxxx>
> To: <collins@xxxxxxxxxxxxx>
> Sent: Thursday, October 21, 2004 8:25 AM
> Subject: {Collins} KWM2A Microphones
>
>
>> Hi to all...
>>
>> I about to finish the restoration of my KWM2A, the radio is now  work=
> ing
> very
>> good, my last problem is find the right microphone, the manual says  =
> "
> High
>> Impedance microphone" but how much is that?.
>>
>> I test the radio with a Normal Z microphone, about 600  Ohms, and
> speaking
>> normaly I only have 40- 50 Watts in the output, if  Im speak loud, th=
> e
> KWM2A
>> reach 100 Watts.
>>
>> Maybe I can use a  microphone preamplifier, but Im afraid about
> overloading
>> the first microphone  amplifier, or maybe Modify the  input in order =
> to
>> accept a low Z microphone ( but my "purist " soul refuses to  make th=
> at
> hi
> hi).
>>
>> Thanks in advance!
>>
>> Pedro XE1YZY
>>  M=E9xico City.
>>
>> Sponsored by the Collins Collectors Association
> http://www.collinsradio.org
>> Nets: Tues: 3.805 Mc-2000 Central / Thur: 3.875 Mc-2000 Central
>> Fri: 3.895 Mc-2000 Pacific / Sun: 14.263 Mc-2000 UTC
>> 1st Wed (of the month) AM Net 3.880 Mc-2000 local (ET, CT, MT, PT)
>> Sun AM Net: 29.050 Mc-1200 Central
>>
>>
>
> Sponsored by the Collins Collectors Association http://www.collinsradio=
> .org
> Nets: Tues: 3.805 Mc-2000 Central / Thur: 3.875 Mc-2000 Central
> Fri: 3.895 Mc-2000 Pacific / Sun: 14.263 Mc-2000 UTC
> 1st Wed (of the month) AM Net 3.880 Mc-2000 local (ET, CT, MT, PT)
> Sun AM Net: 29.050 Mc-1200 Central
>
>
> =
>
>
> Sponsored by the Collins Collectors Association 
> http://www.collinsradio.org
> Nets: Tues: 3.805 Mc-2000 Central / Thur: 3.875 Mc-2000 Central
> Fri: 3.895 Mc-2000 Pacific / Sun: 14.263 Mc-2000 UTC
> 1st Wed (of the month) AM Net 3.880 Mc-2000 local (ET, CT, MT, PT)
> Sun AM Net: 29.050 Mc-1200 Central
>
> 


Sponsored by the Collins Collectors Association http://www.collinsradio.org
Nets: Tues: 3.805 Mc-2000 Central / Thur: 3.875 Mc-2000 Central
Fri: 3.895 Mc-2000 Pacific / Sun: 14.263 Mc-2000 UTC
1st Wed (of the month) AM Net 3.880 Mc-2000 local (ET, CT, MT, PT)
Sun AM Net: 29.050 Mc-1200 Central






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