[AMRadio] Kenwood MC-50 mike with AM gear

John Coleman jc at pctechref.com
Mon Jan 12 16:33:29 EST 2015

Hi John, A lot of the old rigs did not even have a coupling capacitor to the
grid of the preamp stage.  This is of no consequence when using a
crystal/ceramic microphone, but other mics may drain your grid bias on the
preamp tube and cause a lot of distortion.  If the coupling cap is not there
put one in. .01 to .05 is good.  Also a lot of the modern microphones have
way to much bass response for the old rigs modulator and modulation XFMR. A
coupling capacitor in series with the microphone cable and a resistor across
the cable on the rig side of the coupling capacitor will reduce the low
frequency response. Start with a .05 uf and 100K resistor. Decreasing the
value of either will reduce low frequency output and vice versa.  Don't
worry about matching impedance.  The 1 or 2 meg resistor at the preamp grid
is there for what is known as contact bias. And it works well with the
crystal/ceramic microphone as they actually  have their best response with
no load or very high resistance.

Good Luck,
John, WA5BXO

-----Original Message-----
From: AMRadio [mailto:amradio-bounces at mailman.qth.net] On Behalf Of John
Sent: Tuesday, January 06, 2015 11:25 AM
To: amradio at mailman.qth.net
Subject: [AMRadio] Kenwood MC-50 mike with AM gear

I have a Kenwood MC-50 mike and am wondering if I can use it with my older,
tube type AM gear, like the HT-32a, Valiant or DX-100?  Otherwise if not,
will need to get a old D-104, etc.  Any info would be greatly appreciated.

John W6ZKH
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