{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




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                      "K7VS Van"                                       =
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                      <wa7fab@xxxxxxxxxx>              To:       <XE1YZ=
Y@xxxxxxx>, <collins@xxxxxxxxxxxxx>                                    =
 
                      Sent by:                         cc:             =
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                      collins-bounce@xxxxxxxxxx        Subject:  {Colli=
ns} Re: KWM2A  Microphones                                             =
 
                      stserve.com                                      =
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                      10/21/2004 12:08 PM                              =
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                      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






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